Funny thing is, that with the OM gear that I used for 30 years, two bodies and three lenses, I was very happy, and didn't feel a strong need to upgrade or change. There was always a slight urge, but not enough to make me open my wallet. Now, there's stuff everywhere. Still, I mostly use three lenses (17-50, 80-200 and 85) and two bodies (S5 and D80).
I'm very happy with the S5, but it lacks resolution, which is a problem, since I sell photos on occasions. Some of the Nikkors are great too (85/1.8, 105/micro and 80-200/AF-S), but I miss small, fast, good quality primes, like the ones I used with the OM system. Size is a problem. I travel a lot, and carrying all the gear is tiring.
Plan A is to buy a Pentax K-7 with a few primes, the 16-50 and the 50-135. I'm a bit skeptical with regards to the sensor, but I have to try. If it's good, I'll buy another body and more lenses. Size, primes, viewfinder, ergonomics, in-body IS and weather sealing are the key selling points for me.
The alternative would be Olympus. I was very happy with the E-1, and I still have the 11-22, but the E-3 is such a big, bulky box, or at least that is the feeling I'm left with every time I try one. And there are hardly any primes, except my little collection of OM lenses, but they are all manual focus, and none are really wide on 4/3
Lately, I've started using the OM-3 again. I can actually see myself buying another body, since the current one is a bit tired. I would even like to buy more lenses (I have seven now, spanning from 21 to 200mm), but the ones I would like are the expensive ones.
Conclusion? I'm kind of half happy. I don't think a Pentax will solve every problem on earth, but in combination with a Nikon/Fuji system (or Sony, if I can afford it) and OM for film, I'll probably have most bases covered. I might also buy an Olympus body for my 11-22. There's nothing like it anywhere