Haven’t used Last.fm in anger in a long time. But that’s because I spend so much time immersed in my own collection! (Tagging and organising is a bit of an obsession and occasionally I have to start over again, out of sad choice.)
They do really well at pulling together obscure but related music and do it much better than iTunes Genius, though. Not really sure about their genres, but as they pull together very similar tunes when I put a name in, I think they must be getting something right.
I really loved Pandora up until they discovered I was based in the UK and blocked access, and the old Napster service (post-peer-to-peer but before they decided to be a “cloud” service) was really good at turning me on to new music as well.
Spotify gives me the same sort of matches that iTunes Genius does, so not too impressed, but my daughter loves it as she’s really into American country & western.
By the way, thanks for the work you are doing on Jaikoz; it’s one of the few music applications I find myself coming back to. dbPowerAmp being the one I use to rip my CDs, yours the one I go to for first (and second and third) round of tagging.