> Application uninstalls are as trivial as dragging the application to the trash bin. No, this will not eliminate the application's data from ~/Library, etc, but 98% of the time you don't want that anyway.
When uninstalling an application, you usually do want to remove all of the application's components. How often do you say, "You know, I'd like to uninstall 25% of this application, even though the remaining 75% will just be dead weight without it"?
The two kinds of things there are configuration/settings, and the user data. When you uninstall Adium (for whatever reason), uninstalling the chat logs from the last five years is probably not part of your expected outcome. Uninstalling an application shouldn't reach into your homedir and delete things, either on Linux or OS X.
I do expect when I delete, say, Steam, it won't leave 20 GB of games I can't play sitting around in a totally invisible place. Similarly, when I delete some video or sound editing software, I don't expect it to leave several gigabytes of samples and filters lying around. Both of these are real situations I've encountered when people came to me asking why their hard disk was so ridiculously full.
I can understand not deleting things out of ~/Documents, but a lot of stuff that goes in the Library folders is not what users think of as data that should outlive the application.
Steam itself is sort of a package manager, so that's an interesting edge case...
However, I think that there are basically three categories of application data
1) Documents -- These should never be deleted and are not invisible
2) Settings & other small data not worth deleting, probably nice to keep around in case you ever re-install. Most stuff.
3) Large semi-temporary files, like samples and other downloaded add ons that are optional parts of the application
I think OSX handles 1 & 2 well, but you're right, it needs a way to handle #3 too. However, I think that #2 is a much better default than #3.
I can see arguments both ways on things that are technically recoverable but might require lots of download time (like 20GB of games). However, your settings in those games (if not held on Steam's servers; I don't know where they are) should never be deleted by the application. If you're saying that non-recoverable settings and such should go in ~/Documents, I disagree with that, too: things in the Library folders aren't what the users think of as data, but they are stuff that the users will be upset are missing if they uninstall and reinstall.
When uninstalling an application, you usually do want to remove all of the application's components. How often do you say, "You know, I'd like to uninstall 25% of this application, even though the remaining 75% will just be dead weight without it"?