Hastert gets it and he is one of the few who do:

Hopes for a quick compromise on immigration were dealt a blow Tuesday after House Speaker Dennis Hastert said he wanted to take a “long look” at a Senate bill offering possible citizenship to millions of illegal immigrants.

Hastert said hearings on the Senate bill should be held before appointing anyone to a House-Senate committee to negotiate a compromise immigration bill. Later, he said he was unsure what the House’s next move would be.

I think that it was probably a combination of :
1. Wanting to remain speaker of the House
2. 10,000 Bricks
3. Recent win in California by a Republican who attacked Bush and Congress over immigration:

Bilbray, a former four-term congressman, said his campaign took off once he began attacking Bush and Senate Republicans for immigration legislation that included a crackdown at the border – Bilbray called for building a fence on the border – along with the citizenship measure.

(Link to first article via Drudge Report)