In terms of performance the GF1 isn't quite up to the standard of a top professional DSLR, but it is at least a match for most of the entry level models, and vastly superior to any compact camera. It starts up in a little over one second, but it does take around two and a half seconds to shut down again. In single shot mode it can maintain one shot a second, while in continuous shooting mode it can maintain three shots a second apparently indefinitely, with continuous focus, which isn't at all bad by any standard.
The GF1 has a 23-point contrast detection autofocus system with face detection and subject tracking, and in most circumstances it is extremely fast and accurate. Its low light focusing is excellent, with a good bright AF assist lamp that allows focusing in total darkness at a range of several metres. However close range focusing can be quite slow, with some hunting around followed by focusing on the wrong part of the subject. Fortunately the monitor is sharp enough for accurate manual focusing. The G Micro lenses have electro-mechanical manual focusing via a ring on the lens, and the monitor view instantly automatically magnifys as soon at the focus ring is moved to help with accurate manual focusing.
No cameras is going to qualify as an SLR replacement unless it can produce SLR-like image quality, but the GF1 has a couple of advantages over previous pretenders to the throne, in that it has an SLR-sized sensor and Leica lens technology. Looking at the test shots I took with the f/1.7 20mm lens I was immediately impressed by the pin-sharp corner-to-corner detail, with not a trace of either barrel distortion or chromatic aberration. Even shooting at maximum aperture the optical quality is absolutely superb. The Four Thirds sensor seems to be perfectly matched to it as well, producing outstanding shots despite the low light and long exposures.
The Four Thirds system is now well proven over several generations of cameras, and the only remaining question is whether or not it can ever match a larger APS-C sensor for image noise control. If the GF1 is any evidence, the answer to that question is "yes". Shooting log-exposure shots in low light at high IS settings is usually a sure recipe for chronic image noise, and some previous 4/3 cameras have stumbled at this particular hurdle, but the GF1 performed much better than I expected, producing virtually noise-free images at 800 ISO, which is what I would expect from a good APS-C digital SLR. See the accompanying sample shots to judge for yourself, but personally I would be very happy to use the GF1 in place of any current mid-range APS-powered digital SLR. As a more portable alternative to a DSLR it is a pleasure to use, performs well and produces great results. The only slight downside is its relatively high price, but it's worth noting that thanks to its huge success in Japan the price of the Lumix G1 has already dropped to under £500 with a kit lens, so maybe the GF1 will follow suit.
In the Lumix GF1 Panasonic has created a camera that I'm sure will come to be regarded as a classic. It really does offer comparable flexibility and image quality to a good digital SLR in a form that can slip into a jacket pocket. Build quality, performance and most importantly image quality are all of the highest order. If the price drops to the level that the G1 is at now then I would seriously buy one.