EDIT: I could be wrong here; read three posts down. Leaving original message here for posterity.
So if after a day, I am at 681mb of page outs, I should go up to 6GB on my iMac and max it out?
This will sound like a cop-out, but it depends on your use patterns--how long the computer was on, what tasks you were doing, etc.
Say, for instance, you opened a large file in Photoshop, which required you to use your swap file. Your system slowed down for a bit, but after that, everything was fine. In that case, you really don't need to upgrade--you only ran out of memory for a brief period of time.
On the other hand, if your system was
constantly swapping out memory, that means it was maxed out all day. In that case, upgrading your RAM would be more beneficial. If you notice frequent slowdowns on your computer, then your scenario is closer to this case.
Your page outs aren't terribly high. You might notice some difference, but I don't think it would be huge. If your goal is simply to eliminate page outs, then go for it, though you should know that it's always possible to exhaust your RAM, no matter how much you have. It just becomes less and less likely the more you have.
Really, what matters is if the perceived difference in speed is worth the cost to you. But if you're seeing page outs frequently in SL, then I would recommend upgrading for Lion.
tl;dr Couldn't hurt