I'm no pro, but I do have a Wacom tablet and have used GIMP and do textures on occasion, so I'll toss in a few remarks:
1. What programs do you use if you make/edit textures and why?
For editing/retouching, Photoshop (CS5). As the name suggests, Photoshop is designed for photos and working with them. It's not really meant as a content creation suite, but it can be used as one.
For creating (drawing, painting, etc) I use Corel Painter 11. It has infinitely better tools for creating images IMO. I do use Photoshop to tweak them afterwards.
2. What method do you use? (Take inspiration from photos, make your own, tweak others etc)
Inspiration from, or parts of, photos. It depends on the content. For a face or some such, I'll use a reference and draw. For patterns, especially gravel or dirt, I'll use filters and stock photos to create what I need.
3. Are there any nifty trick or tips when making textures that you use or think might be helpful ?
I've found the RealTexture Tools (for Photoshop) invaluable in a few ways, particularly for tiling landscape or building textures. They make that a lot easier, and the intelligent tiling is better than some of the blending methods in other apps or filters.