Yep!
Nor have I, but like you, I have always made sure to back up and copy my entire iPhoto library, not just some of the files inside it.
First rule is to backup your library of course
I have never had problems combining multiple iPhoto libraries.
I just recently combined 7 separate libraries, whenever I format my hard drive I'll copy my iPhoto library to storage and date it.
Once I reload iLife, I open iPhoto, File, and Import to Library, point to the folders.
Every photo now in one library.
I'm sure some must have screwed some stuff up before so be careful and backup before doing anything.
Nor have I, but like you, I have always made sure to back up and copy my entire iPhoto library, not just some of the files inside it.