I can't directly answer the question but I get the feeling most memory issues have to do with an individual's use of their system, and not the system itself. I have a 2009 iMac and a little netbook running Xubuntu. The iMac has 4gb RAM and the netbook just a single gig RAM and not even 2ghz processor. The netbook doesn't slow down on me while the Mac is prone to freeze ups. I Could say "Linux is better than my Mac because it doesn't slow down" but that's not fair. They each have their own pros and cons and I don't see one as being better than the other, it's all a matter of preference.

When the slowdowns bother me I look at usage. On the Mac I always have 4 spaces open (the dashboard is not set as a space on my Mac), and at all times I have the following apps open: Mail.app, Terminal.app, Chrome w/>=5 tabs at a time, MAMP, CodeKit, iTunes, and Sublime Text. Then Photoshop is open a lot in a addition to a lot of others that get opened at times. On the netbook I've got a terminal session, Chrome, and Sublime Text. That's it. It's no wonder the Mac slows down. So I'd say look how you use the thing. No machine has unlimited performance and when it comes to memory usage it's a lot like money in that the more you have the more you tend to spend and you never seem to be able to have enough.