I am very surprised to hear that. I have used GMAIL since its launch and by now it is very effective at filtering spam. In terms of false positives (was incorrectly identified as spam), I very occasionally get something good from the spam filter. In terms of false negatives, I get a spam email in my primary inbox maybe once a month, maybe even less frequently. At some point I got spam from ****'s Sporting Goods but I marked it spam and the filtering mechanism learned.

I wonder, is your Gmail inbox separated into primary, promotions, social and updates?