I played with Pentax K10 some time ago but to be honest with you my Nikon D90 and even D40 would laugh at it. The pictures were very dark with good amount of light, shots at high ISo look much better (less noise) on Nikon. The menu was awkward too, but that's maybe because I'm a Nikon guy. Little off-topic, but I also bought pentax waterproof camera a year ago, optio W60 and man, this camera is a joke (it doesn't remember any settings after you turn it off and the default ISO is 3200 which looks horrible, leaked after just couple of uses which of course is not covered under warranty) and after that purchase I am sure I would never get anything from this company. BTW, I bought a new underwater camera this year, Canon Powershot D10 and it eats that shitty pentax on breakfast. And that's why I wouldn't trust anything other than Canon and Nikon when it comes to consumer cameras.
And BTW, where did you see Nikon D90 for $1500? I bought mine online for $1150 with 18-105 VR lens. Think it over, don't rush. It's good to go see and feel the camera yourself (go to B&H for example) you will know the build difference between Canon/Nikon and others. That's my $0.02