i have a massive library, and consume about 2 cds a week - right now im at 13314 songs which is according to itunes 1050 full albums. i store all my music on my secondary La Cie Porsche HD. I occasionally find itunes converts my cds to aac and stores them on my primary hd, while i want it to organize and store it on my secondary drive. I have the default folder placed in my secondary drive rather then the primary. there are lots of lil data base quirks i tend to find. i guess itunes wasnt really made to handle a library as large as mine.
i also find scrolling and searching is slower when my library got past 10000 songs. Im running a 1 ghz AlBook (17 in)
other then then stupid database annoyances, and scrolling issues - i still think itunes is the best thing to use to keep my music collection organized.