A couple of years ago I spotted Kris using a handstrap with his Canon DSLR at Northern Voice 2006. Such a strap can be quite convenient when you don't want to use a full neck strap, and in recent weeks I've thought that getting one would make my grip on my Nikon D50 a little more secure.
Alas, Nikon's own leather strap is stupidly expensive (more than $100 in Canada—you can buy a whole decent point-and-shoot camera for that!). The Canon version was much cheaper, but requires a camera with a bottom strap loop, which few have. Luckily, there was a perfectly acceptable no-name alternative at Amazon. I had to have it shipped to a friend's U.S. post box, since it wasn't available to be shipped to Canada. I received it early this week.
If you look at my camera bottom photo, you can see there's an extra strap hook on the other side of the grip mount, so you can use both the hand and a neck straps at the same time.
What that does mean is, if you use the regular neck strap that way, your camera hangs sideways, but that's fine once you get used to it. Also, the grip mount is well built plastic with key metal bits, but it's fairly large, so if you already have a big SLR, especially with a battery grip, you're heading into the massive Nikon D3/Canon 1D size territory. So check the size of your camera bag before you get one.