My current bike has a 52-42-30 triple and my new bike is getting a 50-34 double. What I did was make sure to get a 12-27 cassette in the back. The 34 chainring with the 27 in back is only a tiny bit harder to pedal than the 30-26 combo I have currently. The bike will be 6 pounds lighter, so that should make up for it!

Check out this nifty online tool:
http://www.sheldonbrown.com/gears/

If you know the size of your old cassette and new cassette, you can use the tool to see how your new gearing compares to the old!