Installing a TWiki (a particular type of wiki) on the company's website. I've used KWiki in the past, but it recently revealed some significant bugs, so we are moving away from it. It does, however, have a brilliant installation system. A short, clear checklist of well-documented requirements to verify beforehand, then you type "kwiki -new" at the command line. Done. It runs off to "teh Intertubes", downloads all the relevant files, installs them, and sets everything up.
Contrast this with TWiki. I'm fairly sure that the TWiki authors would say their directions are also clear and concise. Here's a tip guys. Any installation document which, several times, use the phrase "Explaining XYZ [which is a required action] is outside the scope of this document" is not a good install document. Also, give me a bloody COMMAND LINE CONFIGURE program, instead of forcing me to run it from a browser! It vastly reduces the number of things that could possibly be wrong. Now I'm feeling like a doofus because I've wasted two hours trying to get this thing running and it's still not working.
Idiots. (The KWiki [edit: I mean TWiki, as Snoof points out below] authors and me both.) Grrrr.