Last weekend, I went with the wife to Costco, where she bought the latest Sims add-on pack: Hot Date. And she spent all of her spare time (about 4-6 hours) for the rest of Sunday & Monday vainly attempting to install it. The install went more or less okay, but every time she tried to start The Sims after the install, it would freeze on the splash screen.
I spent most of my time fiddling with the neXtaw UI toolkit, so I only helped a little. But I followed the instructions to the letter: closed every application running in the Systray, used Taskman to stop every service or background process, then did the install. Same result, every time. And no errata on The Sims web site.
And they say Windows makes installing programs easy.