Fwiw, I finally figured out the cause of the 6 to 10 second delays I was getting everytime I updated tags in the media library.
It wasn't that half my library was on a network drive; it wasn't that the other half of my library was on a firewire hard drive; it wasn't that I had several virtual drives running; and it wasn't that my library was too large or corrupted.
The problem was that I had set up a pane for a playlist group in my view scheme. When you have a playlist group pane, the view scheme filters out any songs that are not in one of the playlists - even when you select "All." My solution was to add an All Audio smartlist to the playlist group so that I could still see my entire library in the view scheme. But apparently, having that 30,000 song smartlist in the view scheme pane slowed MC to a crawl every time I edited anything.
I know others have mentioned using playlist panes... I'm wondering if there's a better way to do this?