I have biked the canal 12 times, and it is a delightful bike trip. The path is level (except for 10 ft rises at each lock) and is packed dirt/gravel. You are in the woods pretty much the whole time, which is nice, but there are small towns every 30 miles or so where you can eat or restock. The Canal is a National Historical Park, so it is well maintained and there are free hiker/biker campsites (clearing with well water pump, porta-potty, picnic table, and fire pit) every 10 miles or so. Additionally, there are many interesting natural/historical sites along the canal that make for a fun break from biking.
I've only done the GAP 7 times, but this section is also great - the trail is smoother and has more towns than the Canal, but is still in the woods. The GAP also features the "easiest" 2000 ft climb you will ever do, a number of tunnels, the Mason-Dixon line, and the Eastern Continental Divide.
If you are interested in bike touring, this makes a great introduction.
As much as I hate to say it, I plan to use Facebook to keep track of who is coming, so please find the bike trip event on Facebook (I will be sending a link to everyone I can think to) and join the event. If you don't get an invite, email me.
Still curious? Here are some awesome pictures from the 2010 trip:
And here is a short summary video of the 2009 trip: