I owned a Muirwoods 29er for three years and put about 4200 miles on it, mostly in the rain. If you did a search, you may have already seen my thread documenting the
history of my Muirwoods. It's a pretty decent bike for the price. It is a complete tank, in both the positive and negative senses.
I weigh around 200 pounds. I used my Muirwoods mostly as a rain commuter but also did some short track mountain bike racing with it so I can tell you that the frame can definitely take a beating. I generally left it out in the rain while I was at work and only cleaned it about once every two weeks. I didn't do any sort of rust treatment, and I never had any issues with rust. The fork, being a suspension-corrected 29er fork, makes mounting fenders a bit awkward, but it can be done with a little bit of imagination.
I really didn't like the stock brakes. My 2008 came with Avid BB5's, but from what I hear the Hayes that they come with now aren't much better. The upgrade to Avid BB7's and Avid Speed Dial levers was the best upgrade I made. With that setup, the braking was outstanding. The stock handlebar is ridiculously wide and exceptionally heavy. I also didn't particularly like the Conti TownRide tires, though they held up reasonably well for 2000 miles before I started getting frequent flats. The seatpost that came with my Muirwoods was 300mm, which I don't think makes any sense at all for a bike with this geometry. I replaced it with a 400mm post, but 350 might have worked for me. I replaced the stock crankset too soon to be able to comment on its durability, but I would say that seems, in retrospect, to have been an unnecessary upgrade. The Alivio shifters are surprisingly smooth, and the standard gearing is good for a hilly commute. The wheels that the Muirwoods comes with are nothing special but they held up very well. A friend of mine who also has Muirwoods 29er had some problems with uneven spoke tension on his, but mine were still going well when I replaced them (another superfluous upgrade).
Overall, I'd say the Muirwoods 29er is a dependable and comfortable bike, but it doesn't feel particularly fast or sporty, no matter what you do to it. Three years with this bike was enough to convince me that I personally perfer something lighter and sportier (specifically, a cyclocross bike with road tires), but that's a personal preference. If you were basically happy with your Rincon except for things breaking, I think you'd be happy with the Muirwoods 29er. If you were tired of riding a tank, this may not be the upgrade you're looking for.