I’ve complained about iTunes being slow with large libraries, but I’m happy to say that with Apple’s release of iTunes 8, this problem is greatly attenuated. Tagging, ripping, even checking and unchecking items is much quicker. There’s still a tiny lag, but very short, when I check or uncheck an item. When tagging, things go really fast: whereas before, it could take 30 seconds to change tags for a single album (say adding a comment tag or changing a name in the tags), now it’s instantaneous. I tried changing tags on hundreds of files at once, and that is fast as well; you see the progress, but it’s no longer 5 seconds per file as it was before.
I’m very happy that Apple resolved this issue, as more and more people have been complaining about it. It seems that iTunes is no longer writing the library file for each change; in the past, you could see the file being rewritten, and see temp files being written as well. I suspect that they now write the changes only once after they have finished and increment them with the library file in memory. Whatever they’ve done under the hood, though it works.
One oddity with the new version of iTunes: my Album Artwork folder is more than 600 MB. This folder is used locally for iTunes to display your album art; it’s a sort of cache folder. Before, this folder was about half that size, but the way iTunes parses artwork must have changed. Looking at some of the files, it seems that they are caching files of different sizes for different uses, hence the increase in size. If you back up your home folder regularly, you could exclude this folder (or at least its Cache subfolder, which contains most of the files); iTunes will recreate this if necessary.