It's not true anymore, I'm using free yahoo account with imap settings as follows:
Type: IMAP
Server: imap.mail.yahoo.com
Port: 143 (SSL unchecked)
Username: Yahoo_email
Password: Yahoo_password
Everything else is default. Well I've also checked UNSEEN/RECENT but it's for convenience.
You can add your program and parameters, it's up to you, the required information for the docklet to work is the described above.
Smaky I've found that in last version (0.1.1.0k), the number of emails is showed in the left of the label circle if the number is more than 2 digits. I've tried it in ve