If you are considering going from Nikon to Pentax. know that all Nikon lenses can mount on Pentax using adapters. Might make your move less heart-rending.
There are two kinds of lens adapters: without glass (macro only) and with glass. Cost is $15-30. The macro ones don't affect the optical quality, but do prevent infinity focus. The ones with glass act as a 1.4x teleconverter, and keep infinity focus. It's cheap glass, so there is some impact on image quality that is acceptable to most people, not all. You can use all your Nikon glass, but the G lenses which lack aperture rings would be wide open. I have both macro and glassed Nikon lens adapters for Pentax K, and yep, they work well.
I also have them for MD, FD, and Konica AR, but that's another story. It's a neat trick to use the orphan lenses on a modern body.
There is also a really clever product called MultiMount that I don't see people using much, but it is very very interesting. Instead of a lens adapter, it is a replacement camera lens mount. You swap it onto your Pentax camera body and suddenly you can mount and use Nikon and Olympus lenses, with no lens modifications (need a thin shim for Nikons). You can also mount pentax, of course, with no changes. You can also mount Konica lenses but they focus macro only. You can possibly mount Y/C lenses with mods, to remove protruding stuff. This is all possible because the lens register distances for Nikon and Olympus (46.5mm and 46mm) are very slightly longer than for Pentax (45.5mm), so you keep infinity focus. Actually they focus a little beyond infinity, and the minimum focus distance is a tad longer.
This costs' $100 for non WR version, 117 for WR version. See it here:
Pentax K+ Multi-Mount (WR version) - Adaptist
I want one but I have not gotten around to ordering. I'm a little cautious about playing with my camera. I can hack lenses all day, but I don't want to break my old friend.