twhirl and mouse very slow when multiple account windows open at once

I have accounds for Twitter, FriendFeed, and identi.ca all open at once. Windows XP gets noticeably slower. When I hover and move the mouse over any of the Twhirl windows, the mouse is really choppy and almost unusable. Each window is very slow to respond to clicks and scrolls as well. I get roughly the same behavior on OS X 10.5.4, just not quite as bad as on Windows XP.