Is a "LastName.com" a good brandable name?

Depends on the last name I guess, but if its easy to say/spell then yes

I like the name and can imagine many uses. From surname history database to BB like site with motto the name you pick with is will be the last you will need. I like the ambiguity of the domain as well as how easy it is to remember and spell.

Just in cars brands, you have: Chrysler and Ford. Last names have always been brandables.

Generally yes, unless you had the misfortune of being stuck with most of these - http://www.worldwideinterweb.com/item/5736-the-100-most-unfortunate-names-in-human-history.html

These names are funny.

I agree with "sometimes" especially if you have a unique and easy to spell last name

edit: that link is hilarious