I have a Sony CyberShot H2
as my second camera (my main is a DSLR Canon 400D).
The point&shot camera (H2) is good for taking photos of aircraft parked at terminals or taxiing, but is very slow (shutter and focus) for landings and take-offs (if you want to take speedy photos, forget it!). If you need speed, take a DSLR (there's good and cheap options such as Canon EOS 350D/400D/450D, Nikon D40/D60 or Sony A200/A300/A350).
Sony has the advantage of the body-built image stabilizer - so you don't need to buy expensive lenses such as Canon IS
or Nikon VR
. Another advantage is the compatibility between Sony DSLRs and Minolta DLSRs and Xi film cameras : you can find good and cheap Minolta lenses and use it with any Alpha body.
Unfortunately, Sony cameras produces high noise on pictures taken at high ISO (800 or upper). In this case, Canon is a better option.