I am getting ready to pull the trigger on one of these myself and from what I understand as long as you get a class four or higher you should be fine. For less expensive options look for sdhc cards on newegg.com or tigerdirect.com. Most of the high capacity cards (8-16Mb) are class six, so you should be fine.
By the way, I believe the class has more to do with the write speed than the quality of the image you will get.
I am considering buying a Canon HF100 camcorder, and am having some trouble finding an appropriate memory card for it. I had planned to use the Panasonic 16gb Class 6 cards, but can't find any for a reasonable price.
I was looking for those because they guarantee a 20mpbs transfer rate,and since the camcorder on highest resolution puts out 17mbps,I figured the memory card would be able to keep up. The manual says use class-4 or higher. The Panasonic is the only card I've seen advertised as being able to do 20mbps, yet I can't locate any for less than highway robbery prices.
So I guess my question is 1) is that Panasonic card really necessary for highest resolution? I don't want to deal with buffering issues where the card can't keep up with the camcorder. But if I can get by with a cheaper and more available card, I'd like to hear about it.