Just a quicky,  to get identi.ca working with pidgin:

1.  Enter your gmail address in identi.ca

2.  In pidgin add update@identi.ca as a buddy

3.  You will get an authorise request (or 4 ) just authorise the first one and give it a sane name like Identi.ca

4. Try sending it an IM,  this will probably fail with a message :

Identi.ca: [Identi.ca] Unknown user; go to http://identi.ca/settings/im to add your address to your account

5. Look at what username your message went from in my case it was foo@gmail.com/Home

6. Pop back into the Identi.ca web page for IM settings and change your IM name to what ever it sent it as

7. You will get a message from Identi.ca saying basically click on this link to confirm your jabber id.

8. Click on it.

Done