As you may already know, pkgsrc is a packaging system that works on many different operating systems — not just NetBSD. Linux is included among these. pkgsrc will work fine on most Linux distributions, but IMHO, there are some that are more pkgsrc-friendlier than others (basically because their original packaging system may be limited).
First of all, there is (or was, since the homepage seems to be dead) Bluewall GNU/Linux, which claimed to be a distribution including pkgsrc as its default packaging system. I never got to try it, though.
Secondly, we have Slackware, a distribution that has been around for a very long time (hmm, I remember when I used 3.4, which taught me a lot about Linux...). It is known that its packaging system is limited; maybe not in the number of available applications, but surely in its infrastructure. This is a good choice because you can easily clear the base system of any clutter and proceed to install anything else from pkgsrc. Martti Kuparinen wrote a tutorial about how to do that.
Then we have Arch Linux, a rather new distribution. I recently tested it in its 0.7 version and seems to be fairly good. Minimalistic, fast, and BSD-like (specially in its boot scripts). Just as in Slackware, it's easy to remove anything "extra" from the default installation and use pkgsrc to handle everything else. The little advantage is that you'll have a better packaging system to handle those packages that can't be replaced by pkgsrc.
At last, there is a hopefully ongoing project by Jeremy C. Reed to create a 100804e680kgsrc-based Linux distribution. I'd love to see that become true, but we are not there yet (I'd say it's just a matter of time ;-). You can check a little FAQ he wrote for more information.
Of course, pkgsrc can be used on any other Linux distribution. Personally, I've used it on Debian and Fedora Core. The choice is up to you.