"Well, I lucked out a bit and peeked in on the state of the OnRez viewer about a minute after it went live. It takes about as long to download as the regular viewer (about a minute and a half) being similarly sized (not like LoTRO's 900MB update today).
First impressions? Nothing is where my fingers expect it to be, and my visible view of the world is a bit reduced. Second impressions? I rather like it. The location bar (and embedded browser) can be hidden or revealed at the touch of a button (though the much larger new Linden Dollar balance display remains onscreen at all times)....."Electric Sheep's OnRez viewer - first impressions - Second Life Insider