In my opinion high bitrate (256Kbps and above) .mp3 is good enough, but there is nothing wrong with sharing FLAC. A lot of people do not hear the difference between the two, so they of course prefer the smaller size. Also it does take a while to download.

Don't know about wma. It seems like the spammers just love that format, so it's really hard to find any legit wma files. I have it added to the keyword filter.

A lot of BitTorrent communities demand high bitrate, so maybe that's where you should look for them. The new Limewire Beta is able to download torrents.

http://www.limewire.com/english/content/beta.shtml

One thing I wish is that people start using real encoders (eg. LAME) to encode their mp3 files and dump the inferior WMP