When I lived in San Francisco I used the streetcars to get to work. In general they worked pretty well, except for the day that they launched the automated controls in the Market Street tunnel, and it took me nearly two hours to get to work, instead of the usual 30 minutes.

I probably complained a lot about transit in SF when I lived there, but since then I have moved to cities with even less transit, and in hindsight SF did a pretty good job.

Seattle launched a streetcar line in 2007. I don't know of any specific numbers, but anecdotally it has had mixed reviews. My office was right in the middle of the line. Basically I could walk to either end of the line in about the same amount of time it took to wait for a streetcar and ride it.

From a cyclist's point of view, there have been a number of accidents associated with the placement and design of the rails. They decided to put the streetcar in the curbside lane, instead of the inside lane as it is in other systems. Perhaps they decided they didn't have room for an island for riders to wait on, I don't know. Part of the route is (used to be) one of primary ways to get downtown for cyclists, and there have been incidents of cyclists slipping/getting caught on the rails, with pretty serious injuries. The city has responded by trying to route cyclists onto parallel streets, but it's hard to say how successful this has been. In my case, I rode on the sidewalk, as there wasn't enough pedestrian or vehicle traffic in this neighborhood that there would be many potential conflicts.

I have brought my bike on the streetcar, once. There was plenty of room -- I didn't feel like I needed to fold my bike up -- and it allowed me to skip a couple of scary intersections/take a weird route on the way to put the bike in DH's car which was parked downtown.