This is a very cute and very small little flash drive. But as the other reviewers found, you don't get the full capacity because of the file-system tables and any other software that gets bundled onto the drive. I wiped this drive of the software and formatted as FAT32 (so my PS3 can read from it) and I got 7.48GB of space instead of 8GB. But when memory is so cheap these days can you really complain?
I bought this drive when it was around £24 and now Amazon are selling it for just over £16. Lexar also have a 16GB Firefly and it's selling for under £30 at Amazon.co.uk.
I wouldn't try to fit this drive on my keyring because of the rigid plastic lid, it has quite a thick loop to make sure it doesn't break, but I find it much better to attach it to a fabric lanyard. It's a pity that they don't include one with the drive.
All in all the drive is fast, small and easy to use. It is robust (it rattles around in my bag most of the time and hasn't broken or scratched). The only downside for me is that the loop for the lanyard is on the lid, not the drive, which means it's easy to forget you've left the drive plugged in, because it's so small! It also may mean it's easier to lose the drive, but since the clip of the lid onto the drive is nice and strong I don't think it's a huge problem.