Faster memory card.

The point is that the camera can write to it faster. (The 30mb/s refers to the writing speed, not reading speed) Do you shoot in continuous mode? If so, I feel it's worth it.

 

Check your cameras maximum write speed, that will determine whether a faster card will be helpful in camera. Where faster cards shine is in the transfer of pictures from the card to a computer. A UDMA card with an appropriate card reader really ups the transfer speed to a computer.

 

How many GB of pictures do you take typically? How much time does it normally take to download pictures?

If you take less than 2 or 3 GB it's not like you spend much time waiting anyway...

 

The ultimate guide to CF speed is here:

http://www.robgalbraith.com/bins/multi_page.asp?cid=6007

For the D90 specifically you want this link:
http://www.robgalbraith.com/bins/camera_multi_page.asp?cid=6007-9597

.

 

D90 can't put images to the card fast enough to take full advantage of the fastest card speeds. However, I have no idea about video recording, a faster card might be valuable there (though I seriously doubt it). Now if you had a D3 or a D700 and grip and wanted to shoot continuous bursts of RAW files on the high speed setting, you may want to invest in a faster card; but even then you'd need to be mindful of the camera's max write speed.

SLC

 

i went through the same problem deciding what to buy with my t1i..i eventually bought the sandisk sd extreme III...i forgot what class it is, but i know in the manual it said to get a high class.

just get a bigger faster one just in case, in my opinion.