I noticed that when you watch Videos that the process WindowServer ends up moving up more Memory usage in the Activity Monitor. This will hopefully be addressed. The longer you have your Mac on, the more memory it uses. Currently I'm at 6.28GB used with 6.14GB Compressed. Now I only have a 4GB machine so I don't know how that makes sense. Last night it was over 10GB before I restarted my Mac. But something I noticed is when it gets really high, my Mac gets hot. Hopefully this will be fixed in the next Beta next week.