Pam gave you a great answer. I want to agree with her that the express bus service to downtown and the financial district is great, so if you're working there, public transportation is a breeze.

It really depends where you are going in SF and what time of day. Golden Gate Transit runs buses up to Santa Rosa (north of RP) and the schedule is here. http://www.goldengatetransit.org/schedules/pages/bus-schedul… If you are commuting to the financial district or downtown at conventional business hours then you might find that an express bus works for you. If you are going to UCSF, South of Market, or somewhere else throughout the city, you will have more difficulty. Many larger employers run van pools or car pools and there is a van/bus/car pool lane a good part of the way south along Highway 101.

Last fall Sonoma and Marin County voters approved the SMART train which will link Cloverdale in northern Sonoma County to Larkspur in central Marin County. I used to commute to the financial district from the Larkspur and Sausalito Ferries and that is a LOT of fun if the schedule permits. They are part of Golden Gate Transit as well.

It will be several years AT LEAST before the SMART train is built but many of us are excited about the approval (the tracks are largely in place) finally after many years of defeat in previous elections. There is a link to a blog post I did about the SMART train below.

I hope that helps. Rohnert Park, Sebastopol and Petaluma are towards the southern end of the county and house a lot of commuters to Marin and SF and beyond to Berkeley and Silicon Valley. There is also good airport bus service to SFO and Oakland Airports, but I prefer to fly out of Santa Rosa whenever possible, but I digress! ;)