A few years ago I was coming back from lunch when a coworker looked at a bike whistfully and sighed, 'I wish I were still young enough to get one.' He was in his early 30s and seemed surprised when I told him how easily he could learn to ride via the MSF program. A few months later he was out on a CBR600F3 and having a great time. Motorcycles are popular for recreation in the Bay Area, and they are vital for some of us as commute vehicles.
Required gear - the bike. While a few rental options do exist, they are not practical except for tourists. You'll need to get a new or used bike and it will likely cost you between 2 and 20 grand. Most new Japanese bikes run 7-11, with some smaller ones at 5. European bikes run 9-20, and Harleys tend to run on the high end as well.
Required time commitment - long weekend for basic training. If you already can drive a stick shift, you should be good to go on your own afterwards. Otherwise, it might take some more parking lot practice.
Costs - for the most part, insurance is cheaper than for your car. Liability in particular is nearly nothing. Comprehensive on my BMW runs $130/year, minus the incredibly expensive uninsured motorist option. Certain models (Harley, Ducati) have high theft rates, and super sportbikes will be hard to insure for young riders.
Gear is the last part, and just as important. While it is absolutely NOT an inevitability that you will go down, it is probable. You want leathers, both on top and on your legs. Sturdy boots protect your ankles and gloves protect the fingers. The helmet has been required in CA since the early 90s and so you'll want to stick with the full face design. I sometimes will enjoy the pleasure of going to work in shorts, but the penalty for lowsiding dressed like that is a biggie. Think about them removing you from the tarmac with a spatula. Good pants are key. (Jeans don't really count: some tests have shown them to last for as little as 4ft of sliding)
As alluded to at the top, there is good training available for new riders through the Motorcycle Safety Federation. Funded by the Big 4 of Japan and BMW and Triumph, run in our state by the CHP, they offer a basic intro to riding course based on provided 125cc bikes and an experienced rider course in which you use your own bike. The basic class is required for those under 21 and partially subsidized. For the rest of us, it runs $160 or so. Completing it satisfies the DMV road test requirement and may get you a discount on liability. You should take it. So many people are now that there can be a considerable wait for an open class. If you're willing to go standby, you can shorten it. 1-800-CCRIDER will tell you the closest centers. I've been to the ones in Alameda and Fremont.
my lanesplitting/commuter page