I completely agree on this point - Windows is in the stone age in this respect. Every installer is different, some are buggy to varying degrees from annoying to break-your-system, etc. I'm currently dealing with an issue at work that involves a rouge installer that overwrites a core system DLL in XP with the same DLL... from '98.
I've always thought of package management systems (apt-get, yum, etc) as a big strong point of Linux compared to Windows or even Mac.
All without user intervention. And best of all, they are all automatically updated from the central server. You don't need to check hundreds of different websites to find newer versions of programs you use.
That is user-friendliness. IMHO, user-friendliness doesn't have to be about pretty graphics (although it probably helps). It's about making things easier for the user. I don't think clicking through a bunch of pretty dialogues to remove a program on Windows is more user-friendly than typing "apt-get remove firefox".
There is nothing like that for Windows.
Yes, but this is to be expected in compiling software as opposed to just copying files. It's generally not too bad on modern hardware though. Except for a few obvious packages like Qt/KDE, most things compile fairly quickly.
[emerge, paludis] is just as easy, but it takes far, far longer.