Caught this link to a page on cyanogen's wiki, where some people have benchmarked various SD cards for read/write speed. ... If you're thinking about running nookie froyo off of SD, this could be a useful starting point in determining what brand to buy:
http://wiki.cyanogenmod.com/index.php?title=SDCardSpeedTests
http://wiki.cyanogenmod.com/index.php?title=SDCardSpeedTests