I lost count over 400. Haven't bothered to count them lately, either, as they're all boxed up.
You're where I aspire to be. I haven't been able to acquire as many games as I used to when I lived in San Diego so it's hard to play catchup to guys like you.
I used to go in to Mexico and for every trip I'd find about 10 or 15 games I didn't own. I don't recall ever spending more than $10 on games, either. It was lovely.
This one time I purchased well over 300 games for $100 USD. There were only 30 that I didn't have, but I knew I could get my money back by selling them on ebay. And boy did I ever. I swear there had to be at least a dozen copies of each Mike Tyson's Punch Out, Zelda and MegaMan games.
As far as hulkster's comment on having to blow in to cartridges... If you're a serious collector you get a toploader or you replace the 72-pin connector ($7 part) in the original NES. It greatly reduces the rituals and pains of getting games to load. I paid $90 for my toploader. Kinda nuts, I know... But it's worth it.