For several months now, I've been using my iPhone (originally iPhone 3G, but now iPhone 4) as my GPS for dirt trails on my KTM 690. Figured I should post my experience, incase someone else wants to do the same. The first problem was attaching it to the bike. I've got it mounted on the handlebars using a gym armband and zip ties. My handlebar clamps prevent it from moving around too much, and it's got quite a bit of padding on the back, and a plastic front. It's not water proof, but it'll keep a few creek splashes / light rain away (especially combined with some kind of windshield on your bike). I was worried about it falling out, or damaging the phone... but it never budges while riding, though a couple of times it has slid part of the way out when I crash (even one nasty high side that left me unable to walk for a week, the phone was nice and secure). I've been keeping an eye out for a better mount, but they are all too bulky for my liking. For risky creek crossings I walk the phone across first, incase I drown the bike (i always walk across bad crossings anyway, to check how deep they are). But mostly I just go slow to prevent too much water spraying out in-front of me, and slip the phone into my water-proof tool bag if it starts raining. Of course, if you don't want to look at the map while riding, you can always throw it in your backpack where it's dry. Battery life is very good when the display is turned off, even while recording a GPS track. The next problem was charging the thing. I used it for a few weeks just on battery, but to get good visibility outdoors you have to turn the screen brightness all the way up, ruining battery life (i haven't tested recently, but i'm guessing it will only last 3 or 4 hours with the display at full brightness, compared to 3 or 4 days with the display turned off). I ended up wiring a cigarette lighter socket under the faring at the front of my bike (found a nice compact rugged one at Jaycar), and using a dirt cheap iPhone car charger. I considered modifying the car charger to plug directly into the bike to save on bulk/cost, but I wasn't good enough with electrics to go that far (I've been told by someone who is good with electrics, that any 12V charger should be perfectly fine even if you abuse it with water/mud, and that seems to have held true so far). It's all hidden under the faring, just a coiled wire sticking out the front of the seat, and it tucks under the seat when not in use. Initially it was falling out of the cigarette lighter due to vibration, so I had to tape it in. The next decision was what software to use. The built in mapping app requires 3G internet access due to copyright bullshit, so It's all but useless. At the time, MotionX-GPS was the only real choice, and it still seems to be the best, though there's a lot of competition. It has: proper offline map support, downloads worlwide maps of roads (excellent or ok depending where you live) and/or topographic maps (excellent everywhere) from openstreetmap.org. It uses a format that takes up a lot of space (several hundred megabytes at least), but an iPhone comes with at least 16GB of storage, so that's a non-issue. you have to manually tell it what sections of the map to download, anything you don't download will require 3G just like google maps. stores named waypoints, and lets you navigate to them (draws a line on the map, or on the compass) can record, export and import GPS traces in a variety of formats has lots of useful statistical data when recording a trace (total distance, elevation chart, average speed, max speed, etc) you can follow an existing trace you recorded earlier. I don't know how many traces it can hold, but I've got over 50 at the moment and they've very accurate (creates a new point every couple of seconds) openstreetmap.org is an *open* map, which is freely available to anyone, and can be edited by anyone. Simply upload one of your GPS traces to the website, and it'll overlay it on the editor, so you can add new roads or trails. I'm slowly adding all my local trails as well as nice camp sights/rest points to their website, so there's no need to rely on saved GPS traces. After adding it to the website, a few days later it's back on my phone. Everyone else who uses OSM will now benefit from your work. it can also display google maps or bing maps, if you have 3G access, and there's some kind of marine mapping thing too. This can be handy for planning trips for trails that don't exist yet on any map (and you don't have a trace), but they are visible from google's satelite photo. Simply add a few waypoints using the satellite photo as a guide, then switch to the topographic map before heading out. it also displays your GPS signal accuracy in metres or feet, and will warn you if it drops out altogether, which is nice. Typical accuracy in ideal conditions is 10m, drops to 20m under dense tree coverage. I've never had issues getting a signal even in places where friends have told me their garmin units struggle. Unlike other iPhone apps, it also has some kind of accelerometer assisted GPS system, which seems like a good idea, if it had a motorbike setting. The "bike" setting automatically switches to "car" once you hit about 100kph. Maybe it still improves accuracy over other GPS apps, I don't know. The iPhone 4 is significantly better than the iPhone 3G. Gets a fix much quicker, and sometimes even works indoors. when you have 3G coverage, it can periodically email your position to friends/loved ones, a nice touch if you don't come home from your ride. and there's a bunch more features I don't need. I don't have much experience with any traditional GPS unit, but my iPhone seems to be able to do everything and more, and has some extra bonuses like a good compact camera. It's also "free", since I already own an iPhone (necessary for work), and I'd need to take it with me on all my rides anyway incase of emergency. Having a full web browser is handy too, when you have internet access. Saved by ass when my sidestand engine cutoff switch failed. After 20 minutes of trying to fix it, I looked up advrider on my phone and found it's a common problem on my bike with a simple 10 second fix. The drawbacks are: it's not water proof, but there are many third party solutions available (though I haven't seen one I'm happy with yet in theory it's not very durable (glass front and back), but I've had plenty of crashes and even dropped the phone on concrete a few times. The build quality is impressive (it's still in near immaculate condition). very expensive to replace if you do drop your bike in a creek, or it gets damaged in a crash. home/contents insurance is a good idea! sometimes my handlebar mount's clear plastic cover, combined with my gloves, cause accuracy problems with the touch screen. MotionX-GPS has some small buttons and I often have to push them two or three times, unless I take my glove off.