I've seen this a few times recently. I'm afraid I don't think it's a Yahoo reviewer. The Yahoo-1.0 is the branding of the IE version that was used. Lycos do the same, as I'm sure do other SE's. I've checked a few of the hosts against the entries with this and none of them are pointing anywhere close to Yahoo!.
To detect a Yahoo! reviewer you need to be looking up the host. If host is something like surf.yahoo.com (replace surf as appropriate) then it's a good chance it's a Yahoo! reviewer. Sometimes you can also tell from the referring string. They also normally seem to browse with Netscape not IE.
The other entry you will find in your logs is add1.yahoo.com (or poss. add.yahoo.com). This is a link checker that will retrieve the URL you have just submitted to make sure it's valid. The timing of this entry will coincide with your submission.