I have a similar issue - I wonder if you could recommend a solution for me? Before I installed wordpress just about a month ago, my website already got around 7000 unique visitors per day. Since moving to WordPress, my traffic is up around 40%.
I had previously hosted about 30 customized Blogger/blogspot blogs on my site. When I went to wordpress (2.0.1), I imported each of those blogs into customized WordPress categories. (here's an example: http://mensnewsdaily.com/category/blogwonks/bob-parks/)
Now users are registering as Subscribers in order to comment at a rate of around 10 or 20 new users per day - and by now I have hundreds. It's only going to get worse! I have just ordered a new dual processor server to handle the increase in traffic. That's the good news.
Unfortunately I'm having a number of serious problems:
1. Using the category system to create unique blogs is cumbersome and leaves me in the position of having to make changes for the bloggers every time they want to add or remove something from their sidebar.
2. There are so many users now that when I open the list of users page in the admin panel (wp-admin/users.php) it takes the page two minutes just to load. Is there anyway to divide the list of users so that they don't all display on the same page?
3. There's a glitch in some of the user accounts imported from blogger. For instance, I can't delete certain users and when I try, their user number steps down. (Let's say I try to delete user number 550. When I do, user 550 disappears only to reappear as user 549.) Also, these problem accounts can't be promoted from, say, Subscribers to Authors - doing so only duplicates their accounts into both Subscriber and Author.
There's more trouble, but you get the idea.
What should I do!