Lightroom2.0 is also a raw convertor using the same pipeline as Adobe Camera Raw 4.5. It supports the same cameras as ACR4.5.
Probably 80 percent of my work is done entirely in Light Room, including printing.
Some people have complained of poor performance, hangs, crashes and other maladies even on some high end machines, both Mac and PC. There are some bugs in the program that the Adobe engineers are aware of and are working to squash.
On my modest machines, a desktop with an AMD 2.0Ghz dual core, 2 gigs of ram running XPSP2, and a laptop with a 2.0ghz dualcore,1 gig of ram running Vista, performance is satisfactory.
HTH
Rich