First understand all email travels around the web unencrypted by anyone. You're ISP provider in your local town you buy Internet service from can read it. The larger companies which provides the backbone of the Internet can also read it. Even before the hated Patriot Act someone was likely providing the government with "suspicious" email. It's illegal for the FBI to spy on US citizens, but some company who's directors are connected to some foreign security service might be funneling data to foreign powers, since America is up for the highest bidder anyways. There's a reason Greg Palast's book is called "The Best Democracy Money Can Buy".
Here's a hypothetical example. The government's right hand bails out and takes over GM, while the government's left hand is spying on Ford's executive emails and cell phone conversations.
My brother is a lawyer and I find it odd his company doesn't encrypt their emails. I've talked to Samsung employees whose cell phones and flash chips are examined every time they leave work, (there's a dye releasing sticker they put over the flash slot to ensure you didn't take out the flash card and download company secrets while at work) but do they encrypt email?
A wise company would encrypt. Blackberry cell phones are the best at this. They have enterprise systems set up specifically to encrypt companies email and much of their communication. There's a reason Obama doesn't use an IPhone. The blackberry probably connects directly to the governments security network.
Isn't Gmail different? No. Yes, your connection from Google to your desktop is encrypted by default I believe, BUT when Google sends your email to your cousin in England, it's wide open for everyone to see.
I know what you're saying. "I don't send any private details in email anyways". Good, but here's what you could do. (this is not the only option, it's just the one I've set up for myself, just in case I need it.)
1. Download Firefox's Thunderbird (http://www.mozillamessaging.com/en-US/thunderbird/)
2. Download and install Gpg 4 windows (http://www.gpg4win.org/)
3. Download the OpenPGP plugin for Thunderbird (http://enigmail.mozdev.org/download/index.php.html)
There's documentation available online. Generate your public and private key. Send the Public key to your friend who will use it to encode the email they send you. Only you will be able to decrypt the message with the private key.