Upload & Sell: On
I have an xpro1, a nex 5n, and a gh1 so I can't speak for the OM-D, but here are my perceptions of each system:
Mft- best lens lineup currently available. It's a mature system, and now that olympus has teamed up with sony, they've addressed one of the things that's held them back for years - overall sensor performance. You're still not going to get as much dynamic range or high iso performance, but at least they're now on board with the best sensor maker available.
Nex- Nothing to complain about in terms of output. Their cameras deliver great files, but feel like toys to me. The 5n feels like a total joke of a camera compared to the xpro1, but again, the output is outstanding. They've been behind the curve when it comes to lenses, both in terms of options and quality but they're getting better. Peaking is a nice feature, but doesn't always work as well as I expected (admittedly I haven't played with the settings too much).
Fuji- the newest system of the three and it shows. They still have some kinks to work out (although things like autofocus have already been improved significantly). The xpro1 feels like a camera made by photographers and that's one of the reasons I really like using it. With an added thumbs up grip, the camera is an ergonomic dream, IMO. Large enough to feel solid in hand, and small enough that you don't mind taking it anywhere. High iso ability is easily the best of the three and rivals many full frame cameras. The watercolor issue is a concern, but I think too big of a deal is made out of it. Unless you're printing large or pixel peeping, you'd never even know it was there and even then you sometimes have to search to find it. They have a great road map full of fast primes that will really fill out in the next year.
Really, all three systems have great things to offer. It just depends on what's most important to you. Definitely try to get your hands on them first if you can. Likely, one camera will emerge for one reason or another.