Over in Raymond Chen's blog I wrote a short comment about game installers and letting the user pick their installation directory. You can read it now at The Old New Thing and look for 'Peter'.
Raymond is right: your computer is already making hundreds of decisions for you, and nobody says word one. Then it makes one other decision that has just as much impact on you, and you get upset. That's silly. He's also right that exposing these decisions to the user is expensive: it wastes the time of people who don't care, it sucks up QA resources, and when people set it wrong (and they will) they call and complain. Or they don't call and uninstall my company's product, and I don't like it when that happens.
To put the problem in perspective: do you argue with the computer about the order in which USB hubs are enumerated? Do you ever find yourselve wishing you could load your program into one of your memory SIMs and not the other? Why can't it go in the other direction? Who picked "HKEY_CLASSES_ROOT\CAPICOM.Store.3" as a registry entry anyway? Why can't you pick that, too? And the answer is: because someone picked a way that's as good as any other way, and you just have to live with it.
Let me describe the actual program I work on. It's a sort of program manager that lets you to pick some programs, and the manager application downloads and installs them. One of our big advantages over the "classic" way of doing things is that we try to have a very smooth download and install experience with no pointless pop-up messages. I recently had the mispleasure of installing the same three games (that my company doesn't control) on a half a dozen laptops. In each case there was just dialog after dialog -- please pick a directory to install to, HEY! THAT DIRECTORY DOESN'T EXIST! OMFG, THE WORLD WILL EXPLODE! DID YOU REALLY MEAN THAT? -- would you like the program to actually work? -- would you like us to spam you? -- would you please read a this long text and mindlessly click OK? -- you have to scroll to the bottom first!. Yuck, yuck, yuck.
So what about the comments people left? Well, my company is picky about what programs are offered, and only allow programs that work when installed to %PROGRAMFILES% and in standard user mode, so Alexey's comments don't apply. We also handle the namespace issues that Will raised. I'm dubious about the namespace collision issue anyway -- the registry would have the same issue, as might the class names, along with the 'universally writable data' directory in c:\ProgramData. As far as disk space issues go (like SuperKoko and Igor Levicki raised) -- well, the programs aren't very big. cjm thought I had a bad attitude, but I don't. Indeed, my bosses often appreciate my general willingness to work on what needs to be worked on. cjm also denies that it causes more work, but that's not true and I have the bug reports to prove it.