Gmail vs. Yahoo! Mail

Gmail pros:

- Free secure POP & SMTP
- Can use "." and "+" to create semi-disposable variations
- Semi-disposable variations can be created on-the-fly when needed (no advance set-up)
- SMTP sent mail is stored and viewable in the web interface

Gmail Cons:

- Filtering doesn't recognize "+" variations
- Semi-disposable variations expose the base email address
- Can't send emails from semi-disposable variations

Yahoo! Mail Pros:

- ($) Address Guard: disposable email addresses
- SMTP can send from disposable addresses
- Extra email address

Yahoo! Mail Cons:

- Essential features (POP and Address Guard) are not free
- POP and SMTP are not encrypted
- Address Guard disposable email addresses must be created before using them
- SMTP sent mail is not stored and is not viewable in the web interface

UPDATE (8 Feb 2007): A more general comparison is at TechCrunch: A Comparison of Live Hotmail, Gmail and Yahoo Mail

UPDATE (12 Feb 2008): Premium Yahoo mail accounts now have encrypted POP and SMTP (may not be available to all customers).