This is also what I had heard from young on, that the blood groove was to make it easier to take the weapon out of the body. Combat blades often have them, including most bayonets, so I figure there must be a functional reason for them.

Thanks for answering the questino regarding the "saw back" on the sgian dubh. They didn't really look like you could use it to saw anything, but my fingers flinch when they go beyond the cross guard. Something to keep in mind, although, putting your thumb on the blade seems like a bad practice to me, esp. if you own any double edged blades. I could see myself forgetting that I'm using my boot dagger rather than my sgian dubh.

Thanks for the enlightenment, Nick!