There are a lot more limitations of pentax than that Oggy. I know there's a lot of snobbery on both sides but you can't act like they're flawless.
The small community means that lenses are harder to come by.
There is Pentax user forum who have plenty of stuff for sale, and Pentax is sold by Mifsuds/FFords etc.
The small market means its a lot harder to source new lenses, particularly third party lenses, and when you finally do find them, they're often a lot more expensive.
Here's 34 from Sigma alone. Pentax also have an excellent range up to 300mm.
There aren't any full frame Pentax cameras which means that the only path upwards is to change systems (Pentax do make a medium format 645D but that's a whole different story and the K-mount lenses won't help you there)
Also with Ricoh's takeover of Pentax, there's no guarantee they'll keep their DSLR line going.
Agreed about the FF, but the quality of the K5's sensor goes some way to mitigating this.
There are advantages to using the Pentax system, such as sensor image stabilisation (versus lens stabilisation), but generally I think you'll find that if you're choosing a system off of the bat, you'll want one with a guaranteed upgrade path.
Agreed, but I would be very surprised to see Pentax pull out of DSLRs.
If your old lenses are primes, then going with Pentax might be worth the drawbacks, but zooms in particularly are fairly useless, with slow autofocus, slow apertures and generally underwhelming performance, particularly on the extremely demanding smaller modern sensors.
I understand that Pentax have addressed slow AF problems in their latest models, but even so I have Canon for things distant or moving fast but keep coming back to my Pentax for other work. After all, cameras are simply tools for jobs and different ones excel in areas.