Kaith,
Just a thought on those seemingly dead accounts and the idea of culling them completely from the userbase. I think it would be better if you add a flag in the db for inactive status and just set the flag when accounts go 'inactive' around the 6month mark instead of deleteing them. This way you can maintain an 'active' count by changing the sql to something like;
SELECT * FROM USERTABLE WHERE INACTIVE='FALSE'
The reulsting recordset will give you active versus inactive for counting purposes and allow users to come back and keep their user names if they do instead of allowing for someone else to snatch the name when the accounts are deleted. On a board like this you may have lots of lurkers who are regged but not logged in or not very active and only post if they are really inspired to do so which may be rare. As the userbase grows those usernames become harder to come up with... just take a look at slashdot for example. Over there I have a uid in the 4 digit range and one with a very low six digit uid. I can't imagine trying to grab a handle on that site now that uids are in the high 500,000's...
Just a thought to consider.
Peace,
Sandor