Gmail gives you tons of mail storage, considerably more than other providers. You can also send larger files through their servers. I don't profess to know all the GOOD details, but 1 CON keeps me away.
Gmail uses intelligent technology to scan your mail messages (data mining at it's finest) and they say they don't snoop, but this technology creates links to advertisers, based on the information gathered from your messages.
It tailors the advertising you see on your screen to what they think your interests are based on your message content.
I think advertisers are already pushing their way into our heads relentlessly enough, and they don't need a free pass.
This is a boondoggle for Google. Why wouldn't you give away millions of free email accounts if you know corporate spies are willing to pay you a fee for every person they spy on? They tell you right up front that they're gonna spy on you, so it's no secret.
If you feel ok with that, then Gmail is a great deal.