Anyone remember how many seats the Republicans were supposed to lose in 2002? 2004?
Honestly, I think they were predicting a wash in 2002 or slight Democrat gains and the Democrats ended up losing several seats, largely due to redistricting. In 2004 they also predicted the status quo and that's what happened outside of Texas, with a few incumbents (Burns, Hill, Crane) knocked off for personal reasons or because the partisan pull of their district went too far in a Presidential year.
The Democrats often led in the generic poll earlier in the year, but not by as much as they have in some polls this year, although the last few polls have shown closer results. Polls before election day in 2002 showed Republicans leading in the generic poll in some cases.
So, 27-30 is definitely the outer edge of predictions right now, but they haven't predicted apocalypse for Republicans in the past like they are this year.
I have been hearing the GOP losing the house since 96....