That was my experience also. My ~/Library/Application Support/OmniFocus/Perspectives folder was empty after the update. Instead of rolling back to 1.6.1, I restored the Perspectives folder from yesterday's Time Machine backup, and now the old perspectives are again back in the menu with SP 1.7. They are not, as you mentioned, in the toolbar but that's easy enough to fix.
Edited to update: Now they are gone again! I suppose I should try to put them back in once again and edit them immediately, but SP 1.7 is doing something to purge the Perspectives folder at some point after it launches.
I just tested with a new user account, and that all seemed to work just fine… but then I went to check my own Perspectives folder, and I see it has also gone missing! So there's definitely a bug somewhere in the sneaky peek, and we'll try to get to the bottom of it as soon as possible.
Any help anyone can provide on reproducing this would be great—since, as I mentioned, I wasn't able to reproduce it with a new account (and I'm not sure exactly when my own folder went missing).