From the first day I accepted an invitation to create a Gmail account, I've been forwarding my e-mail from my other accounts so that I can take advantage of it's search capabilities and to be able to access my e-mail from anywhere.  Aaron Skonnard lists some of the awesome benefits of forwarding your e-mail to Gmail.

Another huge benefit I've discovered is using Gmail's POP access to get my e-mail on my smartphone (Windows Mobile 2003).  I was getting very frustrated with the amount of spam I was having to deal with on my phone.  Since switching my phone to access my GMail account, I believe I can count on one hand the number of spam messages I've received in the last three months.  I love it.