I was all set to do so and then went to the forum and a number of people are complaining about the darkness of the new window set-up, plus various other changes. So I am sticking with 1.6.1 for now.
I haven’t noticed any problems. I probably prefer the new interface.
I have.
I’ve noticed two things so far: one is that, as far as I can tell, the overall appearance hasn’t altered. But that may be because I had modified the appearance of mine in the previous version, and either my theme has “stuck” or the new theme has moved towards what I had.
In addition, the icons for various Applescripts disappeared from the toolbar, but it has been a simple matter (via Customise Toolbar) to put them back.
I didn’t have any Perspectives set up, which seem to be source of discontent at the moment.
But I admit I haven’t played with the new version much.
Ah, change! 
H
Edit: I’ve now had the chance to read some of the exchanges on the OF forum. It seems that if you had a “theme” (i.e. a set of styles for the main window) in version 1.6, then that will stay for 1.7 — hence little change for my copy. The complaints about “darkness” seem to centre around the revamped view-bar — not such a big deal to spark such a kerfuffle, I’d say.
Nope, no problems at all…
It’s fine for me, and I like the new look. 
Okay, then it’s settled. I’ve installed Snow Leopard and I’ll take the plunge and upgrade OmniFocus tomorrow.
Like leaping off a cliff. 