Dave Prior has an interesting post in his blog, DrunkenPM talking about the Post Modern Project Manager.
The quote I liked was when he talked about a project manager "Getting past the point where you consider one approach to be the “one true way”, and on to a place where you see each approach as viable and important"
Just as each project is by definition unique, we need to think about how we approach each project, rather than trying to shoe-horn a standard approach every time. It might be waterfall or agile or spiral or somewhere in between, we need to figure out the best way to get it done.