Just received the first batch of stuff from Play.com - the rest was a separate order so probably next week. No problems at all, the 4gb stick works, shows as having 3.69GB formatted capacity, seems reasonably robust, and file transfer speed seems to be about average. One minor nuisance - there's no loop for fixing it to a neck strap, key ring, etc., but I can live with that. At a fiver it's a pretty good deal.
later - just realised that there's no light to indicate it's getting power / transferring data. Again, not a huge problem.