To add another voice to this review, I just bought one of these as well, the 2gb version. I had bought a 256mb Firefly when they first came out and really liked the small size and how the lid / cover attaches to your keyring, and the flashdrive just snaps out of that. Unfortunately it ended up being much too small on capacity, and the larger versions (at the time I think only 1gb) were more than I wanted to spend. A few months later I ended up buying a Sandisc Cruzer Micro 1gb that was on sale for about $25.
The Sandisc is thinner than the Firefly, but is longer and the flashdrive attaches directly to your keychain, meaning it doesn't simply pop off your keychain for use. It also has a 2 piece soft rubber cover, a long piece for the body and a short piece for the top / cap. This cover is terrible, it comes off in your pocket or simpy from rubbing against your keys, I at one point tried using super glue on it to keep it on which helped for a little while, but eventually the cover started popping off again. I finally gave up and started carrying the flashdrive without any protective cover or cap on it. The drive itself works fine.
Anyway, back to the Lexar Firefly. Last week I was at Walmart and they had the 2gb and 4gb versions in stock for $30 and $60 respectively. I decided to go with the 2gb because of the cost and because I hadn't filled the 1gb card, so didn't feel I really needed much more space. I use mine for mostly small items like webpages, resized images (usually as jpgs), word doc / PDF files, and PSD files of ads I've created for display on a monitor (hence fairly small file size) - with a few large files here and there. I generally move 5mb-10mb worth of files at a time so hadn't noticed the speed issues like Alberto. I will have to test my three drives to see how they compare.
Ok finished testing - these are write speeds only.
Lexar 256mb - 3.88mb/s
Lexar 2gb - 3.68mb/s
Sandisc 1gb - 3.89mb/s
That does seem kind of slow by today's standards...just did a quick search on Buy.com and many of the flashdrives don't list speeds, but the few that do range from a low read speed of 6mb/s up to 24mb/s, and write speeds from 3mb/s up to 24mb/s. All of them use USB 2.0.