As a semi-pro poker player (meaning my car payment and groceries are paid by poker, my mortgage by a Real Job (tm)) let me tell you that only the absolute worst stocks are "Like Vegas"
When you lay a bet down, you either win and keep your bet plus whatever the odds lay you, or you lose it all. Period. With stocks, even when you lose you can pull out a significant fraction of your "bet". Of course that means your chance of doubling up or better is also reduced, most payouts are a fraction of your original "wager"
As far as GM goes, I don't really daytrade but more weektrade. I got in at 31.61 and out at 33.35 before it fell, -but- that was a ten day holding. Unfortunately I could have gotten a full point less four days after my buyin.
As for in/out 30.50/31.80 on Friday that's really close to the absolute low followed by the short peak less than an hour later and I would be curious if you used any strategy or just gut feeling (which would put you closer to the gambling right there)