According to Roger  <rogerb@localhost.localdomain>:

    When *shooting*?  Probably not, unless you do a lot of
burst-mode shooting with lots of shots in a burst.  (I don't know what
the buffer size is in the 350D, and of course it is in part a fucntion of
image size (JPEG quality or RAW).  But when shooting in burst mode, once
the buffer fills, the camera has to slow down to a frame rate which
allows it to write out an image to make room for the next one to be
taken.  I, personally, have never encountered the problem with my D70 --
but I don't do much in the way of burst shooting.

    However, assuming you have a full speed (e.g. USB 2.0) card
reader, you will probably notice it in how long you have to sit around
before 1 or 4 GB of images transfer to your computer.  That is a *lot*
of data -- at any speed, and faster means that you can get on to doing
other things sooner.

    I, personally, have never experienced a failure in a CF card.
Some have experienced filesystem corruption -- but that could be the
camera's firmware instead.  IIRC, there was a problem in Canon's
firmware about a year ago, compounded by triggering a glitch in the
Lexar cards with that camera only.  Lexar replaced the cards in question
(rather slowly, but they did), and upgraded the firmware on the earlier
returned cards to supply to the later return owners.

    Enjoy,
        DoN.

Unless you're trying to shoot a "movie" with your 350D you won't notice any
difference. For the same $$$, I'd suggest getting a bigger card over a
faster card any day of the week (including Sundays and public holidays)

For info on card performance with your camera, read this:

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

Click the drop down menu on the right and select your camera to see
results. Some of the data may seem old, but it's all relative and still
relevant to your choices.

Personally, I chose a fairly fast card not so much for the camera, but
for the card reader. The camera buffers images so unless you shoot very
large amounts of bursts, the buffer will handle the slow cards.

But when I transfer the images to my computer, I want it to be fairly
quick, so I chose a card for that purpose. I'm using Sandisk Ultra II
cards which are almost as fast as the Extreme cards but costs less.

Thanks to all for your responses!
Respectfully,
Roger