I too wondered about that, so a Extreme IV Sandisk card was on sale for my camera and I bought it.
I really don't see any difference for the kind of shooting I do with my Canon 40D. Such as Weddings, portraits, Family get togethers, Birthdays and things like that.
Maybe the pros that do sports and things where they shot in bursts it may help.
The thing I noticed is get a good card reader for your computer as that will really help.
They are inexpensive and worth it.
I am planning on buying a new digital camera soon (Canon sd1100) and was wondering if a high speed SD card would make a difference and was worth spending a little more money compared to a typical SD card. Will I actually be able to tell a difference with this camera or is the high speed memory meant for more advanced cameras? Will this reduce time between pictures? Thanks in advance.