Erica Ogg of CNet informs us that hot on the heels of the $500 price cut for the MacBook Air's 64GB SSD, Dell is offering a 128GB SSD for $600 in their "Latitude, XPS, Alienware and Precision laptop models." I'm glad to see these things moving toward more reasonable prices so quickly, perhaps thanks to recent news of Samsung's cheaper production of parts, but it can never be quick enough. [CNet]
In answer to each of your questions: in certain situations.
Battery life alone is not a good reason to upgrade to a SSD; there are tests showing SSDs help, and tests showing they hurt.
Performance is a mixed bag. Boot time, application launching, and multi-tasking each see a significant improvement when moving to a SSD. Reading from the drive is fast, because there is no spinning platter to slow things down. Writing to the drive is slow(er), because there is no spinning platter to speed things up.
The good news is that most people read from the drive much more than they write to it, especially for home use.
Lack of heat/noise are other good reasons to upgrade to a SSD; supposedly MTBF, but like battery life, that is another topic up for debate.