Adrian,

We are somewhere in between. We create a requirements document then all the stakeholders formally approve it. After that all the changes go through change control and impact analysis, etc. before ending in the spec.

After the go live date, any requests for update are logged in another system. Then when the time comes for the next release, we first sift the logged update requests, then combine them with the new requirements and start from the begining.

I don't have an experience on an Agile project, but have stumbled into missing documentation, bad/wrong comments in the code, etc. issues at many places (The nice exceptions know who they are.) and that made me a huge fan of documenting all requirements, assumptions, wishes, etc.

Vessela