Just noticed this, thanks to a recurring visitor* with fixed IP who seems to have upgraded recently.
Old Opera: Opera/9.80 (Windows NT 6.1; WOW64) Presto/2.12.388 Version/12.16
New Opera:** Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/31.0.1650.57 Safari/537.36 OPR/18.0.1284.49
or, on my own computer (there's an eighteen already? who knew): Mozilla/5.0 (Macintosh; Intel Mac OS X 10_6_8) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/30.0.1599.101 Safari/537.36 OPR/17.0.1241.53
You got that right. The webkit-based Opera's UA says "Safari" (as does Chrome's) AND "Chrome" (will this now be shorthand for "non-Safari webkit") AND ... OPR.
The new Opera may or may not retain the old Opera's cookies. (My outside visitor's first webkit Opera visit was cookieless. Tested on myself and it came through with cookies-- but it's possible I've been here before after installing the webkit version. I've got a variable IP so it's harder to check.)
* Until I went back and checked, I didn't realize how recurring: it's got to be between 10 and 20 separate google searches since July. Mercifully they finally seem to have remembered the bookmark function :) ** Lacking evidence to the contrary I have to assume it's all the same computer. Maybe multiple machines in the same household; I found a few MSIE 10 mixed in. But it doesn't seem to be a school.