My girlfriend and I went to Mexico in August of '07 and were in a little town about 15mi from Puerto Vallarta. Against the wishes of the resort and paying the taxi drivers $$$, we took the public buses too/from town and never had any worries. $1 each way. You couldn't beat it and I never once felt concerned for our safety during the day or night.
1998 Triumph Daytona
2007 Suzuki S50