I recently ditched all my DSLR gear for an Olympus PEN E-P5 (the high-end PEN model). Main reason for the change is that I wasn't taking all the bulky SLR gear out often enough just because of the bulk.
I love the PEN. Phredd made a good point in that if the Olympus had a Fuji sensor then it would be pretty much perfect.
I chose the PEN over the EM-1 mainly for aesthetics, although the EM-1 is a gorgeous looking camera also. The main downside to the PEN is that the electronic viewfinder is an add-on, rather than built-in. Obviously the EM-1 has weather-sealing as an advantage, but I can live without that. I believe the EM-1 also has an updated image processor.
On the plus side, the PEN (and presumably the EM-1) has the most astonishing image stabilisation I have ever used - you can get sharp photos down to half a second, or even slower with a steady hand. The auto-focus is extremely fast to the point of being practically instantaneous.
I currently have the 12mm f2.0 lens, the 17mm f1.8 lens, and the kit 14-42mm f3.5-5.6
Although the plastic body of the kit lens feels very lightweight, the results are surprisingly good. The 17mm and 12mm are premium lenses, and are excellent in low light.
Despite my being used to a range of quality zooms and primes on my DSLR, I have had the 12mm lens on the PEN for the vast majority of the time. It's encouraged me to move myself around to get the best angle, and it really is a great 'general purpose' focal length (it's the equivalent of 24mm on a full-frame camera).
I'd be very interested to try out the 12-40mm f2.8 Pro lens, although it would probably look massive on the PEN.
As for the EM-1 being a good way to 'get started' with M43, I'd say you're pretty much jumping straight in at the top, but if you can afford it, why not?