I'll try to keep this short and sweet as many of you have posted excellent points!
Short of the overall quality of the image and possibly a touch better AF...and the Video capabilities, what can you do with the 7D that you HONESTLY cannot achieve with the 50D?
The bump in resolution from 10.1 to 15 MP from the 40D to 50D, was significant in giving photographers a little more cropping room. However, the 50D and 7D images are nearly identical.
IMO - you're better off saving your $ for better lenses or additional photography equipment instead of changing from one cropped sensor to another. High ISO - Banding... is even apparent in the best cameras if completely pushed to their limit.
So, the EXTRA stuff you get in the 7D...is it worth paying the extra $ for what you can usually adjust in Post? Plus...what and when are you going to print larger than a 16 x 20? Now-a-days, people are forgoing the prints for placing the image on digital media outlets where their high resolution image is automatically scaled down to a 50-100 kb file....
Be realistic and practical! If you were looking to start photography, then I would have a completely different point of view than if you already own something that is very good! Learn to use your equipment to it's max...and just then, when you're needing more than what your current camera can offer...than make a decision to upgrade.