I tend to go with an unwritten rule that recips should be able to comfortable run three abreast within a 750 wide table. But if Greenguy, or Jay, & a handful of others decided to switch over to 900px wide recips, I'd redesign my pages to accomodate them.
But I'm not a submit whore so I don't come across huge recips. I probably should be, but lately I've only been submitting to 9-12 lists. I'm such a loser.