I have a cheap card that I got with the phone and a more expensive one (Sandisk UltraII)
Personally, with the Kaiser, I can't tell any difference between the two. Not when transferring files to/from my computer and not when using the actual device.
However if I compare the two cards in my cardreader on my computer there is a world of difference. (The UltraII being roughly 6 times as fast as the generic one I got with the phone.)
I don't know if it's just my phone or ROM but to me it doesn't seem as if the Kaiser can actually utilize the extra speed at all.
Of course, the Kaiser having an utterly slow USB connection doesn't really help either so maybe there is a difference when it comes to usage on the actual device. If so I just haven't noticed yet as the only transfer heavy stuff I do if pushing files to and from my computer which (I guess) might be hempered by the USB connection.