I freezed some times recently and it was on buisy servers. after I had a lot of framedrop (wich isn't usual) just a couple of minutes ago I was on a buisy servers with some cheaters in it that were heavily bugging the server, and I ran @ 10fps or something, (or it was the map, unlikely becouse there wasn't built on it) a lot of players crashed before me (probably the same bug).
so all times it happened to me (4 times?) was after heavily getting framedrop, and that's maybe why people with athlon processors survive it longer so the chance of freezing is smaller?