The security of it is entirely situationally dependent, I think. Personally, my appletalk network is considered insecure to begin with, and the distinction between guest access and cleartext or twoway random for legacy access isn't enough to bother (and arguably less secure than guest), so I just give guest full privs and away I go. A school is probably different, corporate networks are different still. So, it's all up to the end user. I would argue that discussion about the security of legacy protocols and authentication mechanisms like this within the context of modern computing is splitting hairs, but ultimately everyone has to take responsibility for their own systems.