The main plus in my opinion is the price. It is the cheapest DSLR available (or is it to be available in the nearest future?). For the price of a prosumer digicam, you get to try out the latest DSLR technology and it comes with a very respectable Zuiko Digital 14-45mm lens which cost $400+ if bought separately. So even if the Four-Thirds system failed to take-off eventually, my losses would be affordably low.
The SITEX offer make the price even more attractive. The E300 will come with 2 nos. of 1G 80X Lexar CF cards and a Olympus Pro-Bag. At current CF prices, that's another $300+ savings on CF cards alone. All that means that a 8M DSLR body can be had for <$1,000
I also like the fact that these Zuiko Digital Lenses have a Smart Lens Design and are the only lenses that are have firmware that are user-upgradeable by direct connection and downloading thru the internet. Zuiko Digital Lenses store data in the digital firmware file allowing for software-assisted correction of geometric distortion anomalies like pin cushion and barrel distortion. In fact, it seems that with these data, the camera itself can perform the corrections automatically. And this would explain why some reviewers found essentially zero barrel or pincushion distortion from the Zuiko ED 14-54mm zoom when tested with the E-1.
Another feature unique to the E300 is that both the pop-up flash and external flash (FL-20, FL-36, and FL-50 flashes) could be used together. No other DSLRs currently available could do this. While one of the latter two flashes could be used to bounce light off a wall or ceiling, the pop-up flash can still be up and available to apply fill flash. The pop-up moves not only up, but also forward to keep from hitting the shoe-mounted external flash. According to Olympus, this gives the flash greater ability to peek over most lenses for better coverage of close-in subjects.
The minus would be the prices of Olympus' higher end Zuiko ED Digital lenses and the currently limited range of lenses. Sigma is coming out with 3 '4/3' lenses (18-50mm f/3.5-5.6 zoom, 55-200mm f/4-5.6 zoom, and an 18-125mm f/3.5-5.6 zoom) though. Those with deep pockets can however look forward to the new Zuiko ED 7–14mm f4.0 ultra-wide zoom, one of the widest in the world for “100% digital specific” zoom lenses. The new range of lower end Zuiko Digital lenses like the Zuiko Digital 40–150mm f3.5–4.5 (equivalent to 80–300mm in 35mm photography) are quite affordable though.
Both the VR/IS/AS and Dust Reduction systems are 'good-to-haves'. Unfortunately, no camera system has both of them together and only the Olympus has the Ultrasonic Dust Reduction system in their Four-Thirds DSLRs.
Most users could actually take perfectly good pictures without the help of VR/IS/AS and might not miss anything if they do not have VR/IS lenses or AS camera bodies. However,
ALL DSLRs suffer from image sensor dust problem sooner or later. So you come to your own conclusion on which is more important.
The way I see it, although Olympus currently does not have an image stabilisation feature in their DSLRs, that does not mean that they could not eventually come out with a lens that has IS built-in like those of Canon and Nikon if they so desired that will work on their existing camera bodies. Conversely, image sensor dust reduction systems must logically be inbuilt into the camera body and could never be retrofitted into existing camera bodies.