For this message I am going to stick to the original posters questions regarding a dSLR but from a mirrorless point of view. Since all of my experience with mirrorless has been with micro 4/3 that is the system in focus (pun intended). Micro 4/3 is also the most popular and largest of the mirrorless systems.
To look at Panasonic's G3/G5, GH2/GH3, and Olympus E-M5 we would not know they are mirrorless, they look like SLRs right down (up?) to the pentaprism hump. Picking one up still does not change the perception, all the normal dSLR controls are there including the dial for "Auto, Aperture, Shutter, and Manual" modes. All of these also have a dial for adjusting exposure, thus so far there is still no difference between these and a "true" dSLR.
All of these also have a real viewfinder besides the LCD on the back *but* looking through the viewfinder is where things change. These electronic viewfinders (EVF) are *large* and bright, especially compared to APS-C dSLRs. The EVF can show much more information than a dSLR, including a live histogram. For someone learning photography this is a big help for sorting out exposure.
All of these cameras (afaik) have 16MP sensors and excellent image quality. It is true that all things being equal (and they often are not) the smaller sensor will not equal the image quality of the larger APS-C sensor, just as that sensor will not match Full Frame and that sensor will not come up to Medium Format. If it is all about image quality we should all be sporting Phase Ones, price/size/weight be hanged. But it doesn't work out that way, we compromise based on many factors. For DW and I it was the size and weight that convinced us to go from our Canon dSLRs to Panasonic G3s. Something to consider: perhaps 99% of consumer printers stop at 8.5 x 11 and 16MP micro 4/3 sensors have more than enough data to print that size at best quality. The larger sensor is just not that big of an issue for most photographers.
The system: lenses from 7mm to 300mm (14 to 600 in 35mm equivalent); fisheyes; f/0.95 low-light; 300mm mirror telephoto (does anyone else think it's funny to put a mirror lens on a mirrorless camera?). Even a tilt/shift lens has been announced. Many of these lenses are professional quality, on par with Canons and Nikons best (and on par with their prices too). Panasonics 25, 7-14, 12-35, and 35-100 are top quality lenses, Olympus 12, 75, and others are as well made (and as well priced).
Wait a minute, Panasonic *and* Olympus?
Yes, Micro 4/3 is a standard and any manufacturer that buys into it has fully compatible products! My Panasonic body works perfectly with Olympus lenses. As for third party, their micro 4/3 lenses are not reverse engineered (as they are for Canon and Nikon) but *fully* made to the same specifications as the Panasonic and Olympus products! Third party for micro 4/3 now includes Sigma, Voigtlander, SLRmagic, etc. Even Zeiss has shown prototypes.
As a professional system Canon and Nikon may still have more options but micro 4/3 has enough options to fulfill almost any lens need.
The lens story is not over yet: because of the short distance from lens to sensor almost any lens will fit micro 4/3 (with an inexpensive adapter). Although most of the lenses lose autofocus we can mount Canon, Nikon, Pentax, Leica, whatever to a micro 4/3 body.
To wrap up this message that grew too long, for someone who wants a starter system they can grow with, Micro 4/3 offers good entry level cameras and lenses along with a path to more professional equipment. Just like Nikon, Canon, Pentax, Sony...
I do not mind discussing and debating these points but for anyone who has not done their research first I may be short and to the point!
