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Is the Google Plus widget down? What's going on with that?
Gunther D's profile photoMichael Russell's profile photoGary Crabbe's profile photoCarl Donohue's profile photo
no issu here. just shared your blog post (directly from your blog) to g+.
Click my name to see
nop. lemme make a screen shot of what i have. brb
Thanks .. that's so weird .. I'm getting those 404s on both sites, on 3 different browsers. And both widgets point to different G+ profile/page .. so who knows what kinda gremlin is going on.

One thing that could be affecting what you're seeing is the caching plugin, which serves up older caches pages .. weird.
I have Firefox set to not cache. ever! Ran the test on it.
Your comp might need a quick cache clean up.
The cache isn't anything to do with your browser at all .. it's server side.
hmmm... if it was server. I would, everyone for the matter would see what you see. no?
I have this issue some time and all I do is get rid of all caches.
Your site is acting/viewable normally.
Has you can see no error messages. (Warning Code In red if it would be)

Browsed it on 3 different comp PC and Mac (Chrome, Firefox, Safari) no 404 error.
unless what you're seeing is a cached page .. and I'm seeing, because I'm logged in as an admin, is an uncached page .. but I don't know how that works with calling the g+ widget anyway ... either way .. it's weird that I have all 3 browsers showing a 404 .. it's only for that little G+ widget, not the pages themselves.
Everything looks good on my machine too - but as you said, I am getting an old cached file:

Cached page generated by WP-Super-Cache on 2012-04-29 22:05:28

While there may be an issue at least your visitors are not currently seeing it!
This is what Chrome tells me: "Google Chrome's connection attempt to was rejected. The website may be ... "
And when I go to widgets plus, I get a 'maintenance' page .. that's the problem.
If you go to the page they have a page explaining their current issues - though they seem a bit more extensive than they indicate.
Ha ha ... well, I SHOULD beat you to it .. it's MY website. :)
I just noticed mine is messed up; lost it's transparency so now is just a big ugly white box.
it still seems to be down .. this is lame.