We had an IBM 1GB Microdrive. Broke shortly after a trip down a very bumpy gravel road in a Ford Focus. Seemed great before that.
Our SanDisk Ultra 256MB is very good, but our non-Ultra SanDisk 512MB is very slow. The Ultra takes 7 seconds per image (31 second for 5) and the non-Ultra takes 12 second per image (61 seconds for 5).
I have three brands of CF cards: Sandisk, Eagletec and PQI and they all work fine with my D100. But my friend just came back from a trip in Tibet and he used Canon D60. He found that only the IBM Microdrive 1 GB and the Sandisk 256 MB CF cards worked well in Tibet, but the 256 MB CF cards from Eagletec and PQI cannot function properly. We don't know the reasons.
The DSLR cameras used in the study were made by Canon, but I believe it illustrates the point that the vaious cards perform quite differently, depending on the camera (and its internal bus architecture). I find it interesting that no matter how "FAST" the read/write speed was for most cards, the CP990 and the D30 could not take advantage of the faster speeds (although, the EOS 1D did). Anyone noticed this difference between the D100 and the D1?
I own 256MB Sandisk Ultra, Lexar 12x, Viking, and Ridata cards. All perform very nicely - the Lexar is probably the fastest (for me). I owned a regular Sandisk card, but it just wouldn't work in my S1 (but it did in my CP990). Go figure...
...256 Mbyte CF cards. I have both SanDisk and SimpleTech, and both seem comparable in write speeds. Right now, 256 Mbyte is the bargain point for large CF memory: you can purchase these cards for less than $100 if you hunt around the big online houses. I've encountered no problems yet. At 75 JPEG fine shots per card, these seem big enough. I spent the whole day at the zoo and still didn't completely fill two cards with usable shots. (Although I did do a little editing of clunkers during a lemonade break.)
I've always used SanDisk cards. I've got three 256Mb ones for use with the D100 plus 192Mb and 128Mb ones that I've used with the D1 for over two years. They're rather slow (as noted above - it doesn't really bother me) but I've not had a single problem with them.