are both useful. Also, try Yahoo Groups. Groups are invaluable when you are a reptile owner.
With any pet, but especially with reptiles, it is important to get your information from as many sources as possible. Every "expert" is bound to have a different way of doing things and the only way for you to decide what is best for George is to become as informed on his care as possible. Believe me, it makes it a lot easier!
It sounds like you are doing an above average job already. Mygala has offered some great advice as well.
Box turtles are really not that easy to take care of. I'm not sure exactly what species you have but I do know that most North American varieties appreciate a high amount of humidity. Insufficient amounts of humidity can cause a variety of metabolic problems and it can also affect shell quality.
Like has been said before, dietary issues are another chief cause of shell problems as well as insufficient UVB.
When you say a piece chipped off though, unless it has exposed any flesh underneath I wouldn't be too worried. Turtles often suffer from shell accidents and are surprisingly adept at overcoming them. Just make sure you keep the area clean and be careful with George in the future since he seems to be rather fragile.
A photo would do very well to help understand exactly what happened to George. You should be able to rescale the photo in any editing software on your computer -- you should have something. Microsoft Photo Editor comes with XP if you have that. Open the picture in the default editor and under "image" usually there is a command called "resize." Resize the picture until it can be viewed at 100% in your browser without having to scroll and this should be sufficient. Choose the "save as" command to save it without having to change your original.
If you are still worried about George or if the shell damage appears worse than I assumed then you should take him to a vet with experience with reptiles.