and they don't reply, do you consider it rude?

I do.

I'm not talking about huge bands who obviously don't update their own myspaces. I'm talking about bands who perhaps you're doing a gig with and you send a note to say hi and they just blank you. I always take it as them saying 'we're a more important band than you and will not deign to reply'.

Surely the whole point of myspace is to cut out the middelmen between bands and fans etc?