Based on what we see in the books:
pure-blood= entire family is made up of wizards/witches (although I'm not sure how squibs fit into that or why there is an accountant Weasley)
half-blood= some muggle relation- at least a parent or a grand-parent. Harry is referred to as half-blood even though both his parents are magical.
muggle-born= non-magic parents (This would be Mark if no one else in his immediate family is magical)

blood status according to the hp lexicon: http://www.hp-lexicon.org/wizworld/b...tus-names.html

I'd imagine that a lot of people would be half-blood since it seems tough to be pure-blood. It wouldn't surprise me if it's someone new or someone that people haven't really noticed.

Yeah, Mark Evans was the only possibility I could come up with. I really hope he's of some significance (or at least involved the last two books in some way). It is way too much of a coincidence that he shares the last name.

Actually, you're missing out on a rather large character (pun intended) who is a half-blood--Hagrid. After all, only one of Hagrid's parents is a giant and Rowling has said that Book 2 was originally going to be called "Harry Potter and the Half Blood Prince." Couple that with the fact that she has said that there are clues for Book 6 and 7 in CoS (i.e. the exposition of Hagrid's expulsion from Hogwarts), it all adds up.

I suppose I was thinking of Hagrid as half-breed instead of half-blood, but there really isn't any reason why he can't be considered both if the JKR's definition of half-blood includes have any non-wizard/witch parents or grandparents. But if it's just part muggle parentage then Hagrid probably doesn't fit.

Ugh I really hope it isn't Hagrid. I seriously got annoyed with Hagrid in the fifth book. More Hagrid would be horrible, in my opinion. I'm hoping Hagrid bites it in book six, or at the very least stops teaching. Grawp has to have some other purpose though, so it wouldn't surprise me if it is indeed Hagrid.

Great discussion about Hagrid. Maybe he is somehow a prince of one of the giant tribes. However I'm hoping the title refers to Neville. I think something big is in store for Neville in the final books!

The problem with it being Neville is that he seems to be pure-blood. But I agree that it would be great to see him get some pay back for what happened to his parents and I really want to know what's up the gum wrappers since it seemed to mean something to him in the hospital and JKR has them all over her site.

Hagrid does seem a bit too stupid for his own good. I don't want anything bad to happen to him, but he has been making himself less likable.

I doubt the "prince" is technically a prince, it seems more like it would just be a term of respect, but who knows, either way I'm certainly looking forward to it.

Nothing. She screwed up and used a name that she shouldn't have.

Godric Gryffindor (from the "lion" comment and all)

That was my thought as well. He very well could have been an animagus too. I suspect he is the HBP. Harry pulls his sword out of the sorting hat in the chamber. The lion symbol and sword seem to lean towards this possibility.

Could it be the new Defense Against the Dark Arts teacher? I assume whats her name won't be coming back this year.