I don't have any SD Card testing kit and have no idea about bit rate transfers or what class card is best - and NO disreaspect is aimed at those who have gone the extra mile, thanks guys.
In the real world, for the money, this wee beastie was a must buy! I chucked it into my Blackberry Pearl 3G and copied around 250 albums. Took about 20 minutes and i still have 16Gb spare - that's enough for at least one whole season of Chuck. As soon as i get it, it's going into my Blackberry Curve 3G and i guess it'll do the same job in there too.
So in a nutshell - Lots of storage and you can copy stuff onto it quickly (it takes a 4Mb MP3 track in about 6 seconds from what i saw on my Windows Media Player Sync screen) and it's stupid good value for money.
Yeah I'd buy one of these again if i ever fill the first one.