I woudn't say Compiz itself is a pain - but when you combine Gnome with Compiz and with some applications, then there are some issues.
From my experience:
Using Compiz and playing Counter Strike (with Wine) and running Google Earth and playing a movie at the same time together with features like rotate cube works perfectly fine for me.
But Nexuiz for example has issues. It totally captures input, so Gnome thinks computer is idle and a screen saver kicks in. I had to use a script to disable screen saver just before the game starts and reenable it after the game exits. Also Nexuiz-glx has issues with sound suddenly stopping for no reason, while Nexuiz-sdl does not have sound issues, but it does not work with Compiz - I have to switch to Metacity.
And so on...
Some apps just work without any problems, while others have issues. It is no ones fault - just lack of full compatibility. And I still talk about things that happened to me in LM6 64-bit - I expect the same things in LM7 unless the devs decide to rewrite Gnome, Compiz, and 10000 other programs in addition to building Mint
Btw. Will there be a smooth transition from RC1 to Final?
I had an orgasm when I saw this topic