I've been playing with PTAssembler also. Its free to try, and costs $39 to register.
One hint on taking the shots is to take a couple test shots to get a good exposure, then set the camera to manual exposure. This ensures that all the shots are exposed the same. If you don't do that the seams can be pretty obvious.
Shots with different exposures can work OK. When you output the final product, you can specify a layered PSD document with masks. You can run a levels adujstment on each layer to try to get the brightness to match. It works well sometimes. If a seam shows in an area like the sky, you can blur the mask to hide the transition.
On shots that have objects closer than infinity, I sometimes turn off the autofocus. The stitches can get messed up if the camera focuses on a closer object in one frame and a more distant object in the next.