I've seen a number of references to a folder at ~/Applications, including in a comment on this question. This prompted me to open my home folder on my Lion installation to have a look, and sure enough, there it is, complete with its own folder icon. Checking another machine which is running Snow Leopard showed no such folder.
So, am I right to assume that this is new with Lion, and is the recommended location for self-installed apps? I never have liked cluttering up the system Applications folder with extraneous software, and for that reason store most non-bundled apps in a self-created ~/My Apps folder. That has the advantage of being assignable to the Finder window sidebar without ambiguity, which is more than can be said for ~/Applications.
Finally, as I write this I wonder if the thinking behind ~/Applications is that apps stored there will appear in Launchpad?