I cannot find a way to restrict the worktypes associates to a project by user, because not all the team members can do all the work types we can find in a project (e.g. a designer does not deploy the DB, a developer does not make the planning, etc.)
So this could be a nice improvement to the tool: Add in the user profile a list to the available worktypes per project he/she has access.
I'd like to see this too. Not only would it control who booked to what but it would also allow me to set charge rates by individuals. At present I can only do this through the use of worktypes (well I think that's the only way!)