Well after some more research, I'm going to kind of answer my own question... please feel free to comment!.
According to one poster, "Class 6 corresponds to minimum 6MB/sec or 40X. This rating is virtually meaningless, as virtually all but the cheapest cards these days are faster than 40X." http://forums.dpreview.com/...forums/read.asp?forum=1010&message=25005210.
However, it may not be so meaningless from a buyer's standpoint, as this poster mentions: "Currently, the fastest-writing digital camera can barely sustain 9 MB/s (60x) in write speed. And some cameras cannot take full advantage of an SD Class 6 card even in continuous shooting mode at high ISO sensitivity settings with fine/superfine JPEGs or RAW images." http://forums.dpreview.com/...forums/read.asp?forum=1010&message=25034802.
The first poster above seems to offer a good conclusion. "Buy at least a 60X name-brand card from a reputable dealer. Sandisk, Lexar, Kingston, Transcend, ATP have been pretty reliable."..
Make sure those speeds you are looking at are write speeds and not read speeds. Many manufacturers will list a very fast (ie 120x) speed but that is the read speed as opposed to a 60x or so write speed..
Of course, you only need a card that can write as fast as your camera can send the data...
I'm confused about how to go about buying SDHC cards. I understandthat there is a "class" designation 2, 4, and 6 which indicateminimum sustained data transfer rates of 2MB/s, 4MB/s, and 6MB/s.But what is the 133x designation for? Is that something different orjust the same speed rated in a multiplier fashion?.
It's probably "times the rate at which you can read data from a CD spinning at 1x CD-Audio playback speed"...
SDHC cards were developed with standards so no matter what brand name you buy is fine. Fast cards are excellent but sometimes overkill if your camera can only write with it's limit. I have a 8gb SDHC and it can take almost 2000 of large superfine pictures on my G7. This would be an advantage on the G9 with it's RAW capabilty...
SDHC classes categories are based on minimum SUSTAINED write speed. They were set with video in mind. The SD Association is dozy and never thought about still cameras when setting the classification. Figures like 133x write speedrefer to the burst write speed and are more relevant to digicams..
The SD Association also failed to plan ahead enough so most cards reach Class 6 with the ink hardly dry on the spec. They did the same with the SD card failing ever to set a spec for 2-4GB cards. Did I say they were dozy?.
*Nikon* D Eighty + Fifty - Other equipment in Profile.