willnorris
commented
12 years ago so the experimental sgapi support (turned on in the options page) does handle the old-style profiles URLs, but I agree that having support for them without the sgapi would be nice.
As for putting the link on your site, I would recommend https://plus.google.com/ID (no trailing /posts or /about, and no /u/0/ segment either)
Just wanted to point out that at least some link to their Google Plus accounts using other URL:s than plus.google.com ones.
I use http://www.google.com/profiles/VoxPelli one on my site: http://kodfabrik.se/ Ade Oshineye uses http://profiles.google.com/adewale on his site: http://www.oshineye.com/ (The WebFinger-implementation on gmail.com also uses http://www.google.com/profiles/VoxPelli to link to profiles - but that implementation seems to be pretty outdated anyway - also links to the Activity Streams on Buzz instead of on G+)
It seems to be pretty tricky to support these older links in the extension though as one can't easily follow redirects through AJAX and especially not through JSONP. One would probably have to rely on some kind of server side lookup - but not even the Social Graph API seems to follow all of the redirects in such a way that it currently works for my site (Works for Ade's site though and adding the "edo"-parameter to the Social Graph API requests solves it for my site as well)
I guess one should probably change to a new id-based URL when linking together profiles - but which URL should one use then? https://plus.google.com/u/0/114892733479367518317/posts or the one without a /posts appended? Or perhaps the one with /about appended?