Yesterday I got my base model MacBook Pro with retina display (8gb memory, 256gb flash storage, 2.3GHz). This thing is beautiful. However, I attempted to install Windows via Bootcamp so I could play Sims on my Windows partition, and let's just say it didn't go very well. This laptop has no optical drive and there's no way I'm buying one for one use so I tried to install via USB and it just wasn't having it. I may wait a while until there are some tutorials out there about doing it from an .iso.

Anyway, since for now I'm stuck playing on OS X, is there anything I should know? Does it run very different? People say it's bad but coming from a laptop that would overheat at the mere mention of 'Sims', surely it can't be that bad?!

There have been tutorials out for creating .iso from DVDs since Vista and USB thumb drives have become prevalent, and maybe even earlier for DVD image backups.
I'd check www.sevenforums.com. They even have a tutorial on slipstreaming your Windows 7 install USBKey with Service Pack 1, which is very convenient if it is already downloaded from a previous install. But in your case, a "virgin" Install version would be sufficient. You'd need an 8GB USB drive and a way to format that to ntfs system.

Are your games in Digital Download versions then, from Gametree or Amazon? Do they have the PC version of the game as well?
Otherwise, you'd still need an Optical drive to install, won't you? Or, redownload gigabytes of game files from Origin in Windows?

For Sims 3 Mac-specific issues, you can head on over to our Mac subforum (the breadcrumbs or the Help menu would bring you there) and see the troubles Mac users are having. There'll be more in the Archived section, of course. And for that, you have to search with "OSX", "Mac", "Snow Leopard", terms etc.
You didn't mention what GPU the MBP has, so how bad is still up for discussion.