tell me about 4/3 system and Oly e 620?

hello,

looking into getting an olympus e 620. I have read about 4/3 system, but really, what are the practical differences/challenges I will find if I switch to that from the standard dslr format like canons/nikons or my current konica minolta a 200?

practical like when I get the images on my computer will they be oddly shaped, or present cropping problems/issues? I will mostly do panoramas from a tripod and some point and shoot stuff.

what I like about this e 620 is the built in anti shake, not from lens anti shake.

can i get a 200 mm telephoto for this camera? not sure I really need 300 mm.

Thanks!
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