We've ridden Muni's new hybrids along both the 27 and 48 routes for a couple of weeks now, and our experience has been slightly mixed. The good aspects are that the buses are sleek and extremely quiet, and their layout seems more ergonomic and conducive to large amounts of people getting on and off on a frequent basis. There are many more straps for standing passengers to grab onto, and every vertical pole has a "next stop" button. The buses are also lower to the ground, eliminating the need for steps, and they appear to be more wheelchair-friendly, although we haven't observed the boarding of any yet. The seats are arranged in a way that makes each one desirable to sit in, and we love that there are now three single-seats as opposed to the old diesels that had only two. The back of the bus is now on a platform -- much like AC Transit's buses, which almost feels theater-like.
[Update: We rode the 48 hybrid again on Saturday after we had read all of the comments in this thread, and here's our addendum:
We had forgotten to mention that three out of the five senior seats closest to the front door also double as the designated wheelchair spot. This means that there are only two remaining disabled seats within reach of the front door, as opposed to nearly six senior/disabled seats on the old buses.
Also, the hybrid on Saturday was especially hot, and it was never in direct sunlight. Half of the windows were closed, but like lhitch said in the comments, we felt way too short to reach them. Ventilation seems to be lacking in these buses, regardless of the A/C issue mentioned in the comments. It might not get hot that often in San Francisco, but the greenhouse effect still applies to Muni, especially when the ventilation is less than desirable.
In regards to the folks who had mentioned how the new buses seem to also lack proper moving-around room, including SFist Jeremy: We noticed that the front area does seem to be constricted by a short wall on the right side that divides the senior seats from the singles and juts way out into the aisle. We're not exactly sure why the wall is there, maybe for wheelchairs, but it definitely interferes with the flow of traffic.
Finally, the back door is a pain in the ass. After hearing in the comments that there was some "laser beam" to sense our hand pushing on the door in hopes that it will open, we lightly touched the yellow part of the door and then waved our hand around. We were the only ones getting off, and another passenger softly yelled out "back door" for us, then finally the door opened. Like jportillo, we weren't sure whether we finally opened the door ourselved or if the driver did...]
See the cons after the jump!