I'm guessing that there aren't a lot of people on Slashdot who are both users and developers for Odoo / OpenERP. I am. I am also formerly a UX expert (late 90's, but I keep somewhat up-to-date), and I am currently an active developer and consultant. I have some very specific views on this based on my background.
1. In the Agile manifesto it says "Working software [is valued] over comprehensive documentation." That has always meant, to me, that UX takes priority over user documentation. I've seen Agile teams kick the snot out of competitors by focusing on UX and foregoing nearly all user documentation. When I say "nearly", I mean that a very high level (well written) orientation document, is sufficient.
2. For this system itself which is a complex ERP system, there are four levels of "documentation" possible: a) User Documentation b) Configuration Documentation c) Customization / Plug-in Developer's Documentation and d) Internal Development Documentation. Since Odoo is open-source, in a way, all of these levels are "user documentation".
3. UX absolutely needs to be the one and only factor in considering the end user experience of an already-configured system. There shouldn't be any need for an end user to go to a user manual unless an organization has done extensive configuration / customization (in which case that organization has the responsibility for the documentation, not the Odoo organization. Likewise, UX should be the main approach to making configuration easy, but there may be some scenario-based examples documented to help orient those who are doing the configuration. These are your day-to-day admin users. The marketing automation module is a good example of where UX sucks and the documentation is poor. Given the choice, I would much prefer the UX to be improved!
4. For customization and internal development, there is still a role for UX to play, but (knowing the actual state of the documentation) you must improve that documentation dramatically. It is sparse and hard to follow, hard to find the right information, and often has very old / outdated screenshots. Although what information there is seems to be accurate, there are often huge gaps, and many undocumented api's and options. I know this because I have had to struggle through creating custom modules by reading through reams of source code in other modules. Love that it's open source, hate the quality of the developer documentation :-)
As a sideways promotional plug, our Scrum Team Assessment tool is built on OpenERP 7.0.