If you customize the toolbar, you can add buttons for your perspectives there, the perspective in use will be marked on those very nicely.
Looks good too.
I would suggest using the Perspectives window to change the icons for your perspectives as well, makes it much easier to tell which is which.
I use 6 perspectives at the moment and this is what it looks like:
http://img.skitch.com/20080708-x4w9r...9ien3hxwwt.jpg
As you can see, the one on the right is in use, the one with the green icon.
By the way, all these icons are from the Buuf and Buuf Deuce sets by Mattahan available at
http://mattahan.deviantart.com/gallery/#Icons
Had to mention where I got them from, since showing off something I didn't make seems a bit wrong, so at least I gave him some props.