I believe it's more important what's going on on your computer while you're playing the game than if it's a new or old computer, Windows or Mac. If you have lots of applications running in the background, the meter may stuck.
I have a small utility in my notification area that shows me the current amount of available RAM. It currently shows 271 MB as I'm typing this. (The overall RAM on this PC is 1 GB.) However, when you play the game (or when you're launching it), it's capable of draining all of your RAM, at least temporarily, so that I'm left with a single-digit figure for available RAM, or no free RAM at all. The crisis usually passes after a minute or so, and the free RAM returns to 100+ MB levels, but the crisis mostly occurs when there are lots of other applications running on the PC besides the game itself. One should especially close any other browser windows except for the one in which you're playing the game. (Windows of alternative browsers should be fine; playing the game in Chrome & browsing the web in Opera works for me, here. I would not dare to play the game in Chrome & simultaneouly browse non-WGT webpages in Chrome.)