I find combining Slimserver and iTunes a headache. I have dual libraries--AAC files for portable iPod and ALAC for home use. The only way of keeping the AAC files out of slimserver and clogging that up (esp. since you can't tell an AAC from an ALAC until it plays) is to restrict the AAC files to a separate directory and *not* use the iTunes library file or to check all the ALAC files in iTunes and get slimserver to only use iTunes checked files. But since you check and uncheck things in iTunes all the time, it means you have to disable the slimserver from updating. Brain damaged either way.
Right now I've separated my AAC files and ALAC files into separate directories, but there are issues there too--I use EAC/iTunes to rip to ALAC, but when I convert to AAC, I've got to copy those files from one directory to another. Total PITA. I thought about resetting the "use this directory" setting in iTunes before doing the AAC conversion, but that seems to take forever, and it scares me because I have no idea what it is doing.
I'm also rethinking my support of the iTunes UI. I really wish the indexing was better and categories could be collapsed--how about a "view by album"? Or "view by album art"? How about a "now playing" queue that can be added to by double clicking on a song, rather than having that cut-off the current song and start the new one?
In some ways, this still has a long way to go...