Like nearly every enthusiastic photographer, I am perpetually debating whether (and how) to upgrade my equipment. The questions to be addressed for any upgrade are: What new capabilities is the the upgrade money buying, and are they worth the price?
My current kit is based around an Olympus E-P1, and features the 14-42 mm f/3.5-5.6 kit lens, the Panasonic 20 mm f/1.7 pancake, and the Oly 9-18 mm f/4-5.6. I expect to add the Oly 40-150 mm f/4-5.6 soon. A version of Olympus' near-legendary 50 mm f/2 macro is strongly rumored to be on the way, and I'll probably buy it on release.
Right now, there is no sensible upgrade path for me in the Micro Four Thirds system. All of the existing Olympus m4/3 cameras use pretty much the same sensor. The E-P2 is essentially the camera I already own (modulo the ability to use the unappealingly expensive external EVF), and the E-PL1 and E-PL2 lack a quality thumbwheel for setting the aperture. Panasonic also makes m4/3 cameras, but after a disastrous experience with Panasonic customer service, I have vowed never to buy one of their cameras again. (Of course, from what I hear about GH2 availability, that's a pretty easy vow to keep...)
So, an upgrade means a system change, and from everything I've seen, the upgrade system for me is Pentax. The K-5 seems to be the camera to beat at the moment, with an excellent balance of size, build quality, pixel count, and low light performance. Other cameras (such as the Nikon D7000, which has a very similar sensor to the K-5) are possibilities, but I'll focus on the K-5 for the moment.
Thom Hogan suggested an enthusiast-level kit based around a K-5. His kit is not entirely to my liking. He called for f/2.8 optics, which are desirable in theory, but are large, heavy, and expensive in practice. In addition, the 16-50 mm f/2.8 on his list seems like a bit of a dog. Also, he has selected a wide-angle prime, whereas I prefer a wide-angle zoom. So, I have made my own list. The total purchase price of this list is a hair shy of k$5. Were I to buy the items on this list, what would I get, and would it be worth it?
For the bodies, I'd trade a smaller (and much prettier) body for one that is tougher and has an eye-level viewfinder. I'd also trade a 12 MP sensor for a 16 MP sensor (nigh-irrelevant) that does about a stop and a half better in low light (a very important improvement). I'd also get a deeper buffer and faster autofocus, but, as I don't shoot sports or wildlife, that's no more than a minor advantage to me. Both cameras have in-body image stabilization, which I almost require of a camera at this point.
For the zoom lenses, I am generally trading smaller size on the Oly lenses for a slightly brighter aperture and a bit more reach on the Pentax lenses (105 mm-e and 375 mm-e for the Pentaxes, vs. 82 mm and 300 mm for the Olys). For the primes, the Panasonic 20 mm is a stop brighter than the Pentax 35 mm, and is much smaller and has a slightly happier focal length for me. On the telephoto end, the Oly 50 mm will be a stop slower than the Pentax 55 mm, but will likely be sharper.
So, am I willing to pay $5,000 for the more flexible zooms and superior low light capability of the K-5 system and move on from my small, light, and elegant E-P1 system?
Sadly, the answer is, "No." As much as I'd love to buy a big pile of pretty new camera equipment, it's just not worth it for me. I guess I'll leave my wallet closed and wait for the upcoming "premium" Olympus m4/3 body...