Udi Dahan talks about the merits of agile methods vs. (heavy) process methodologies (countering a post by Joel Semeniuk on CMMI).

I can't say I totally agree with either (what else :) ) - There are cases where agile methods are a better git and there are cases where you'd be lost without a plan. While agile methods optimize for change (which is indeed a grim reality we all live with) plan driven methods optimize for complexity. Barry Boehm and Richard Turner detail the various people related issues that can make you choose one over the other. The diagram below (taken from that article) sums it up nicely.

It is always important to strike a balance between the level of process employed and the project at hand. That's why even the more heavy processes (like RUP or MSF for CMMI) are tailorable. I guess a lot of organization don't bother to take the effort to tailor the processes to their need and rely on the "out of the box" experience which is not tuned to their needs. and thus suffer less than optimal results.

Another important issue is tool support - If you are going to employ a more plan-driven (heavy) process you really want it to be supported by your tools to help alleviate that "document oriented development" feeling Udi mentioned in his post. This is where this upcoming release of MSF shines (especially vs. the previous release of MSF).