If you have another card to compare against, it'd be helpful to know if the speed of the card is noticeable.
I am in the market for a 16gb card (as this phone is an upgrade/merger of phone and my ancient Rio Karma thats active but mostly dead buttons), as I need at least that space for my music.
As Rastaman-FB said, music and basic phone use seem to be fine on the phone (compared to 3G/internet browsing/case button press), but as I may end up updating the phone w/compcache, I'd like to know whether to spend the extra on the fastest card or if a lower spec is ok and go for size (32gb would be handy).
P.S. My case, with the small inner seam cut has done wonders for battery life.