Pentax DA lenses on Nikon or Canon?

I'm curious if there's an adapter to mount a current Pentax DA lens onto a current Nikon or Canon APS-C body (like a D3100 or EOS T1i). If so, would any features be disabled (metering, autofocus)?

Converters do exist…

But from what I've read they are typically poor optical quality. The converter needs an optical element to compensate for the difference in the distance of the flange (which is longer for Nikon).

There are quite a few offered on eBay.
http://shop.ebay.com/i.html?_nkw=pentax+to+nikon&_sacat=0&_odkw=pentax+da+to+nikon&_osacat=0&_trksid=p3286.c0.m270.l1313

Actually the best bet would be to buy lenses specific to what ever brand you pick. I own a Rebel XS and I own a Tamron 18-200 lens. I've found that, at least in my case, 3rd party lenses just don't perform nearly as well as lenses made for these cameras.

That said, I wouldn't attempt to make this match because I think you'll end up disappointed and buying Canon or Nikon lenses anyway.