True. Didn't think about that. But, the user id is awkward to skip so much like that. It should just insert into the next row (incremental). I don't know how the ids are calculated on an import, whether they use the old forum's ids, or what, but now a new member joining will have an id of #600 or so because of that 300 gap.
People like me that pay attention to the id can see the newest member 10000, but see only 5000 members, and it makes me question what happened: That many spam joins, bans, etc.?