I've been using 3 images for my HDR images. I am now playing around with DSLR Remote Pro from Breezesys which allows me to tether my camera to my laptop and have more control over the number of images that the camera takes. I am going to keep an eye out for a netbook to carry around with me to make it a bit easier for doing the greater number of images.
Al
I use a Dell Mini10V running OSX, and control the camera with Epson's Camera Window. The Dell weighs very little, and has a ten hour battery life. Best of all, I have an "active" USB cable (it has an amplifier at one end) that allows me to be up to 15 or more feet away from the camera. This is helpful, since one of the things I do is take HDRs of streams and creek beds, and it's sometimes difficult to actually look through the camera because of the setup.
One RAW file
Everything you need to know is there!! 
