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i hate the arms length grip too, but the waist level finder replication with a flip up lcd (sony and some olympus cameras) is pretty awesome (preferible to an eye level finder in many cases) and something i can't get from any current dslrs. there are plenty of compact mirrorless cameras that over evfs too (and fuji offers a ovf).
I second what sebboh writes. I shifted from DSLR shooting to mixed Canon/NEX, and now NEX only. Shooting a NEX is a different experience, because it leads one to use a different tool differently. I shoot 85% at waist level, looking down into the tilted up LCD, and use magnification 100% of the time to achieve proper focus even with f:1.4 lenses. My keeper rate from a focus POV is maybe 80%, Vs 40% with a 5DII with Zeiss prime.
As to adapters for your lenses, you have 3 kinds. The passive kind, which is a purely mechanical device. Except that the quality of E-Bay cheapos is quite variable. Some good, some bad; I had one where I couldn't focus beyond 5m...
Then you have "smart" adaptors, optically passive but with electronics that will let you keep AF and IS on your DSLR lenses with a NEX.
Then you can buy a SpeedBooster which does add an optical component, so it is not loss-free, but brings your FF DSLR lenses back to their native focal length, and gains you one stop of speed as well.
The last two categories are not cheap, and I would recommend sticking with proven, quality vendors, such as Metabones.