I've spent many an evening in the backyard viewing overflights with my telescope. I have an 8" Dobsonian telescope, and I suggest you might want to consider one of these as well. The benefit of the dobsonian is that the mount is very stable, and it is also very easy to move quickly by hand - which is essential for airliners in cruise. I find it gives steadier views of aircraft than binoculars on a tripod, even though the magnification of the binoculars is much less.
The best view is achieved when the airplane is "perpendicular" to you - it's kind of hard to explain, but it corresponds to the time when the airplane is closest. At this point you can swing the telescope sideways only - no up and down motion is required, so you can move the telescope at exactly the speed of the airliner and get incredibly sharp views (I have been able to read registrations off the bottom of the wing before). The view at sunset is nothing short of spectacular.
If you have any questions about my technique, feel free to ask. I know there are very few people who spot in this way (my friend and I call it "dot spotting"
), but it's a lot of fun.
Edit: I should mention that I haven't really tried much photography using my telescope, except for with a small point-and-shoot. As far as I know, it should be possible to hook up a DSLR using the right attachment, but I haven't tried it myself. One potential problem I can see is that the camera body and sensor would be open to the elements, since there is no glass at the front of a Newtonian reflector, so dust spots could become a problem. So, if you are looking into this strictly for photography purposes, it would be a good idea to talk to someone knowledgeable about astrophotography first.
[Edited 2005-12-03 22:26:44]
You know the gear is up and locked when it takes full throttle to taxi to the terminal.