OK, I answer with some hesitation because I really don't know personally ... but my accountant had me complete some kind of form so that he could file my return on paper -- I think it was necessary for some reason due to one or more of the following circumstances for 2010 -- we bought / sold a house and had the tax credit associated with that, we did some home improvements that qualified for tax credits (energy saving windows, etc.), and had a lot of donations (of stuff we couldn't bring with us due to lack of space), although I think the latter was NOT a reason that they couldn't file my return electronically. Or it might have been something else unusual on the 2010 return for us.
It clearly was the default / usual practice for the accountant to file returns electronically, but apparently there are exceptions even if you use an accountant who otherwise must use the electronic filing.
Since I haven't done an electronic return with my accountant (yet - but 2011 might work out when I get around to it), can anyone tell me how you sign the return? They actually used to return the forms if you didn't sign them, so at one time a signature was important. I'm not familiar with how "electronic signatures" work (one of the tech-stupid areas of my life). Quite honestly, I don't see why they WOULD care, as long as you sign the check if you owe them money 
Thanks!
--BG
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1.4. Re: W2G
The no paper rule applies to preparers but not to
individuals. This is from the IRS site."any tax return preparer who anticipates preparing and
filing 11 or more Forms 1040, 1040A, 1040EZ and 1041 during
a calendar year must use IRS e-file".