Okay, here's some REAL advice from a local.
1. There are several ski buses in/around San Franciscohttp://www.nacski.com/http://www.bayareaskibus.com/
2. There are a number of ride-share oriented groups based in the SF Bay Area.
The most pre-eminant of these is Snow Pals.
People are always posting ride-shares here.http://www.snowpals.org/
3. Northstar (and other resorts) often list ride sharing and public transportation options on their website (after all, it's to their benefit to get you to the hill to spend $$ on lessons, lift tickets, and food)http://www.northstarattahoe.com/info...huttles.asp#sf
4. I am willing to bet that just about every local ski shop has a message board (Lombardis, REI, Mountain West, Cali Ski Company, Any Mountain). Check with them to see if they offer a ride share message board (more often than not this will be a physical board located at the shop where people tack up notes). Though they might have online forums, as well.
5. Most of the colleges and junior colleges also have message boards (again, usually a physical board located in the studen union). Check there, as well. They might also have online forums, too.
6. You can always post here on Epic and over at TGR and on various ski resort message boards in the "Hooking Up" section and fish for a ride.
MY BAD...the OP was very brief with his/her info. The subject header led me to believe that they were a 23 year old based in SF...upon further inspection it sounds like this is an out-of-towner, right?
Basic info that would help with advice to be dispensed would be:
1. Are you visiting from out of town?
2. Where are you coming from?
3. Are you planning a week long stay or is this just a weekend/day trip?
4. Are you visiting for the first time?
5. Are you just concerned about skiing or do you want some sight-seeing, as well (this would affect whether to suggest Reno, SFO, Oakland or Sacto as a point of entry).
All of this info is helpful in giving you the best advice...I read your post quickly and assumed you were a San Francisco based skier who can't rent a car, thus my advice was tailored to the weekend warrior looking to get up to the mountains.
If you are coming from out-of-state and looking to spend a week or more in Tahoe, then the options are vastly different.
You would probably want to fly into Reno and then take a bus from there to SLT (which is closest and will offer the greatest number of lodging choices). You will be able to ski Heavenly and Sierra at Tahoe without the need of a car. If you want to hit Incline, Mt. Rose, or Kirkwood then you'll have to arrange transportation.
It really boils down to where you are coming from, how long you'll be staying, and a few other parameters.
Another site to check:http://www.slidingonthecheap.com/