In particular, I notice that Twitter user authorization redirects to
the wrong URL.  It ignores the oauth_callback parameter of the first
GET.  Instead, it appears to use the callback URL statically
registered for that consumer.  Also, it appends ?token= to the URL,
regardless of whether  the URL already had a query string.  It should
append & (not ?) if the URL already has a query string.  Also, the
parameter name should be oauth_token (not token).
Forwarned is forearmed. :-)
-- 
Alex Payne
http://twitter.com/al3x