OK that sounds good thanks - having the IS in the lense. The other thing I hear is that Pentax camera's are backwards and forwards compatible with any of the Pentax lenses. Not sure how this is on the Nikon D3000. Should I be concerned about that or are there enough lenses for this camera?
You can use any Pentax K-mount lens on new Pentax bodies, and it works. Obviously, with manual lenses, you lose AF, and with the older ones, i.e. SMC-M or Pentax-M (i.e. where the camera cannot set the aperture), it's a bit fiddly to use, but it works well. With regards to forwards compatibility, it's true for the FA lenses, since Pentax still builds a proper aperture ring onto their lenses (I wish Canon would do this too). I have seen a guy with a brand new FA-77 on a K-1000. But, as with other brands, the lenses that are designed for crop cameras, don't go on the old bodies, so that breaks forward compatibility. In Canon land it's EF-S, Nikon calls it DX, Pentax calls it DA.
The same goes for Nikon, although they have one kink in the story, in that their entry-level DSLRs don't have the screw drive built in, so AF lenses that don't have a built-in motor, such as the 50mm f/1.8, cannot AF on them.
BTW, the sensor shift stabilisation works really well, and the advantage is, when you stick that 40-year old lens on your shiny new DSLR, you still have stabilisation.