I installed Lion on a fairly small partition, because I wanted to keep Snow Leopard around for testing applications and I didn't want to deal with moving all of my music and other files. It went great until I wanted to run Photoshop:
One of the nice things about Mac OS X is that applications just work, no matter where they are. No matter where an application is in the directory structure, if you double click it, it will run just the same as it would in /Applications.
Adobe, of course, follows this rule about as well as they follow all other rules involving "fitting in on Mac OS X", which is to say that they completely ignore it.
However, I wasn't going to take no for an answer. I have 3GB of free space remaining on my Lion partition, enough for about half of a Creative Suite app. Since Adobe's error dialog didn't provide any information besides "it's broken", I was pretty much on my own. After some messing around with chroot (a complete failure), I tried something more obvious.
$ sudo ln -s /Volumes/Macintosh\ HD/Library/Application\ Support/Adobe
/Library/Application\ Support/Adobe
Well, that's a different dialog, and one that sounds like progress. I like to live on the edge, so I did not update.
Oh. Well, never mind. At least their error message tells me what files are missing (it doesn't).
Except, as far as I can tell, it does work. Photoshop didn't quit after that error dialog, and I can open documents, save documents, and move pixels around, which is what Photoshop is for as far as I can tell. A success.