I have a few gmail accounts that I use for various purposes, and earlier this month and last I was looking for a way to transfer the mail that gmail considers non-spam to my primary account. I found that there is a way to transfer all mail (in mail settings), and a way to transfer mail that matches a certain filter, but wasn’t able to flag only the items that weren’t spam.

After asking on a few forums, I was finally able to find it in google groups:

If you’re using filtering to forward your gmails to another account:
In the filter, use “-in:spam” in the “has the words” section. Spam won’t be forwarded to your other email account.

I find this very useful. I have all of my mail pass through gmail’s spam filters before coming to me now.