What did I do wrong - Safari 6.0.5 on 10.8.4 ... has recently taken a turn for the worse. Constant beach-balls, and after an hour's browsing, that damned Safari Web Content is running between 2 and 3GB, between real and virtual. If I leave tabs sit, Safari says it must force reload all pages. 

A little memory-freer app helps release some "Inactive Memory," run frequently, but doesn't seem like a real answer.

Have 8 GB RAM in a 2.8GHz MBPro, and lately big page-out numbers. Did the RAM needed to run all this get ahead of me ... or is this all really Safari? Or Flash, which runs at high memory, but not so high as that "Web Content" - which is what? Another name for Flash?

On broadband, we used to say, Disable caches. Maybe not a good idea anymore. Or turning off pre-fetching?

Restarting Safari returns things to normal, for a while. I run a few extensions, not many. Keep machine in good maintenance. Do not have a problem with keeping many apps open. I just wanna surf!
For what it is worth, I generally recommend to people who don't want to update their OS that they use chrome. Apple only updates safari when they update the entire os, so you are better off with a third party solution for a browser.

(Mavericks came out after this question was posted, so this answer is only effective for people looking for an answer to the question now that it has been released.)