I found some useful info on
Type Capacity Write speed
(MB/s) Read speed
(MB/s) Standard 16 MB, 32 MB 1.3 5 64 MB, 128 MB, 256 MB, 512 MB 3 5 M 256 MB, 512 MB, 1 GB, 2 GB 2.5 4 H 256 MB, 512 MB, 1 GB 9 15
So I guess H is quite a bit faster than older xD cards, but I can't find any actual comparisons of Type M vs. Type H on specific cameras.
I'm asking because I'm trying to decide between getting a 1 GB Type H card and getting a 2 GB Type M card for my F30.
Steve's review of the F30 says, "Rapid shooting in single shot mode captured images at 1.6 second intervals without the flash." That's with a 512 MB Type H card. Since Type H is about 3.5X faster than Type M, that would be terrible if it took 5.6 seconds between shots with a Type M card, but I'm sure that isn't the case.
I would assume that performance is usually about the same, but maybe Type H is a little faster when you have the quality set to Fine.
Looking at the read speeds, though, I'll bet you could tell a difference between the two pretty easily when browsing through pictures in review mode.
I guess the bottom line is that I don't have any real need to get a 2 GB card (I'd need an extra battery to have any hope of filling it), but if the performance isn't much different, it might consider it just in case I go movie crazy.