I've changed it so that it no longer updates all the nicks immediately. Instead, each nick is marked for update, and only those nicks that are visible in the listbox are updated. Nicks that are not visible are trickle updated in the background over time.
This results in a slower channels nick list display if nicks need to be updated but only in situations with thousands of users and a complex nick color list with large user lists/notify lists/etc. This is probably better than having mIRC freeze 5 to 8 seconds every thirty seconds :-)
This change should be in the next version.
