Romney 15% tax rate a political issue?

TPM today is talking about how Romney is admitting that, as a 1%er whose income is almost all capital gains, he pays an effective tax rate lower than most middle class people, on his millions and millions in annual income. I'd say this was a great issue for Democrats, but, unfortunately, unless framed very carefully and well, it probably won't be, because the level of sophistication acceptable in messaging directed to the electorate at large seems to have to be at about third grade level to have any effect, and things like "effective tax rates" are just too complicated. Sad, really.