Open source project management tools the way forward?

We've just spent a load of cash retraining contracts managers on the use of MS Project. Every time we do a quality based tender submission we get asked to show how we develop and update programmes. But how many contractors actually update all their programmes on a regular basis? The problem with MS project seems to be that you need the software to open it, so how can it be used in a truly collaborative way. After all, collaborative programming and integrated teams are supposed to be the holy grail of continuous improvement (if they're not then tell me what is so I can put it in my next bid). Open source gizmos that interface with MS Project and other applications are being developed, and these must be the way forward. The main criticisms seem to be that they have less functions than MS Project, but my Toyota has lots of functions and i don't use any of them. Shouldn't the main point here be not how flashy your programme is (or could be), but who's actually using it as a useful project management tool. I'd be interested to hear about any contractors currently using open source tools, and on what size of projects.