I am starting to wish profiles (like myspace) could have a friendly url attached to them. I don't like the idea of using memberIDs for profiles, as that gets too confusing. I think it should be possible that the login/username is converted into a profile link. Spaces can be replaced with _ or a similar character. I think that would be more user-friendly.

What happens then when the member changes their display name?

Use a custom defined one like IP.Blog does.

What happens then when the member changes their display name?

Nothing, it would be done by login-name or a 1-time settable url

how so messy and unnecessary is that?

Hmmm... the way blog does it is it actually writes the files into the blog directory - that could get messy unless it was something like yoursite.com/profile/your-name, but that might defeat the purpose.