(Of course, I meant "I go to any OpenID client...", in step one!) I may get some
chance to play with this next month and do some diagnostics, but if anyone can 
shed
any light on this one beforehand, I'd be grateful!

I'm having the same issue.  Would love any information on a resolution, config 
change etc.

Had the same problem.  I think it has to do with having non-default permalink 
URLs on.  Try editing:

wp-content/plugins/openid/common.php

around line 619, in the "openid_service_url" function, change the line:

$url .= 'index.php/openid/' . $service;

to just:

$url .= 'openid/' . $service;

That worked for me.

Oh - also, I had been using the "DB Cache Reloaded" plugin, and had to disable 
that to get OpenID working, as 
well.  Leaving it enabled wreaks havoc with the OpenID plugin.  It'd be nice to 
be able to selectively not cache just 
queries made by the OpenID plugin.

I would bet that similar caching plugins might also interfere; try disabling 
them if you're still having problems.

[deleted comment]

Thanks, I'm making some progress now.  Here is the new error:

OpenID login failed: return_to does not match return URL. Expected 
http://www.www.www/blog/openid/consumer?janrain_nonce=2009-11-14T06:19:03ZMwAFtX
, got 
http://www.www.www/blog/openid/consumer?janrain_nonce=2009-11-14T06:19:03ZMwAFtX

It's missing the ".php"  on consumer.  I'm fiddling, but I'm not sure how to 
append .php.

I finally got this working for me. I had to edit common.php, and, in
openid_service_url, change:

$url .= 'index.php/openid/' . $service;

...to...

$url .= 'openid/' . $service;

Now I don't get the odd extra redirect from the index.php/openid to just plain
/openid, and everything works.

I disabled all my other plugins and my openid stayed broken; this was the only 
way I
could figure out how to fix it. Hope this gives someone a clue as to what's 
actually
going on. I'm guessing it's because of the (perfectly standard, as far as I can 
tell)
"disappearing trick" (via mod_rewrite?) that WordPress does with index.php...

Incidentally, I see there's been some code changes in this area with the latest 
release, 3.3.3. However, I still have to change "$url .= 'index.php/openid/ . 
$service" to "$url .= 'openid/' . $service;" to get the plugin to work for me 
(WordPress 3.0.1, standard "Day and name" permalinks enabled.)

At some point, I'll see if I can figure out exactly what gives, but I'm way too 
busy at the moment, sadly...

Is anyone else with permalinks enabled finding that the OpenID plugin is 
_working_ for them? Because that's be helpful to know...

I have permalinks enabled and I can't get it to work even tinkering with this 
stuff. :(

My blog is http://www.happyassassin.net/ . wordpress is actually in 
/var/www/wordpress on the server and there's a 
/etc/httpd/conf/webapps.d/wordpress.conf which has these contents:

Alias /wordpress /var/www/wordpress

<Directory /var/www/wordpress>
    AllowOverride None
    Allow from All

#    Options FollowSymlinks
#    RewriteEngine On
#    RewriteBase /
#    RewriteCond %{REQUEST_FILENAME} !-f
#    RewriteCond %{REQUEST_FILENAME} !-d
#    RewriteRule . /index.php [L]

</Directory>

Wordpress config is set up to match this: Wordpress URL is set to 
http://www.happyassassin.net/wordpress , Site URL is set to 
http://www.happyassassin.net . AIUI, that's all how it's supposed to be. I used 
to have a .htaccess file in /var/www/wordpress with the contents:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress

not quite sure where that came from, but I've temporarily removed it, and it 
doesn't seem to change any behaviour. (My permalinks still seem to work).

I can't get OpenID plugin to work right, whatever I tinker with. If I leave 
common.php exactly at stock, when I try and login via OpenID, it redirects to:

http://www.happyassassin.net/wordpress/index.php/openid/blahblah

which doesn't look right, and all the browser displays is a blank white screen. 
If I hit refresh, it complains that the nonce is out of range or has already 
been used (but I didn't get logged in!)

However I mess about with common.php to change the path, I can't make it work. 
I can get it to try just www.happyassassin.net/openid , 
www.happyassassin.net/index.php/openid , I can even comment out the whole bit 
about rewrites and get it to try the ?openid path - none of it works. Either I 
get the same behaviour as above - white screen, refresh gives a nonce error - 
or I get a 404. I don't get any useful errors in the Apache logs, so I'm kind 
of lost here, I just don't know what's going wrong or how to figure out what's 
going wrong.