Might not be as useful as it could be if it only notified you for exactly correct spellings of your username. For example, who's actually going to type out the full name of, say, xXxHaLoLoVeR117xXx? It'll be even worse if it's caps-sensitive; I don't think I've even once seen someone's name properly capitalized by someone without (near) perfect spelling and grammar.
It's also the case that people with common names like "Bob" or "Fred" would be unintentionally spammed by notifications about posts which don't actually refer to them.
While it's a good idea in theory, I don't think it can be made to also be a good idea in practice.