In general, browsing the web with Flash disabled makes for a more pleasant experience and saves a lot of horsepower on your machine. But it’s a pain switching it on and off for those few sites where it’s important.
ClickToFlash is a WebKit plugin which provides a convenient solution for Safari users. Flash content is replaced with a shaded image saying ‘Flash’. If you click on it, the Flash is loaded and plays, and you can right-click to whitelist a site so that their content always works.
There are, apparently, still a few rough edges, but I’m going to try it for a while and see how it goes.