The higher speed is really only useful for two things:  Burst mode or
rapid fire individual pictures, where the camera gets ahead of its own
buffer used for holding the shots before writing (a faser card allows
faster writing, so this doesnn't build up so soon), or [the main
reason] for downloading the pix off of the card using USB (where a
faster read speed combined with USB 2.0 causes a dramatic drop in the
time needed to download them).

If you very seldon overrun your camera's buffer (and you'll know by the
fact that it refuses to take a picture until it's emptied at least one
more out of its buffer), or don't have a problem with waiting a few
more minutes for a full card to be downloaded to your computer, then go
for the standard speed cards.

If you're going to buy multiple cards (and you should), buy one fast
one in case you ever need the burst mode capabilities, and save money
on the rest of them by buying standard speed.  They're tremendously
less expensive, because the manufacturers understand that many people
have a [sometimes unnecessary and unreasoning, similar] "need for
speed".  This is due to marketing hype similar to the "need for
megapixels" which is often more of a feel-good stroke than a real
necessity.

Ken pretty much summed it up, except for one thing.  In the early days
of CF cards, only the slower speed cards were available (they were
also smaller).  As faster cards became available, the price on the
slower ones came down.

Austin

Thanks guys for the info...really appreciate it.

Chuck.

The why has all ready been covered. This will help with which is how fast:
http://www.robgalbraith.com/bins/multi_page.asp?cid=6007-8197