I agree with what most everyone here has already said. Try packing a little tighter and tamping more frequently.
I think that another problem is that sometimes newer pipe smokers are so excited to try a bunch of different tobaccos that they never stick with one long enough to learn its ways. When you combine that with the fact that different pipes like to be packed differently, because of differences in pipe geometry, airway dimensions, etc. you can see that the variables can go exponential on you quickly.
Pick one tobacco and get to know how it burns in all your pipes. When you've got a handle on it, move to another one if you feel like it. Believe me, there's plenty of time to try everything you want to smoke. It's not a race. If you do this, you'll soon learn to recognize similar cuts and consistencies. You'll pop a new tin of Tobacco Z and think, "Oh, this reminds me of Tobacco X that I tried a couple weeks ago. I know from experience that I should pack this tighter."
If you want a real interesting experience, try smoking some La Brumeuse Semois tobacco. I don't think it's possible to pack that tobacco too tightly! I pack it in my pipes with a wooden dowel and what seems like a ridiculous amount of force and pressure, and it still lights right up and smokes perfectly! You do have to tamp it frequently. It's a real eye opener.
Sorry for the ramble. Hope it all makes sense. My wife is rushing me to leave for dinner....
