Interesting things to look for:

1.  Turn-out.  Heavy turn-out is required for Obama to win.  (It won't happen, but you can look for it.  ;0

2.  Edwards MUST do well in the early returns.  The rural precincts will be reporting first and he needs to really do well to overcome Clinton's advantage in the I-80 corridor where the big cities are.

3.  If a surprise comes it will be noted in these early returns.

4.  Look for turn-out numbers in Des Moines (Polk County,) Cedar Rapids (Lynn County,) and especially Iowa City (Johnson County) and Ames (Story County.)  The last two are home to the Univ. of Iowa and Iowa State, repectively, and for Obama to win there must be an unusually large turn-out.  

5.  Des Moines is the state capital and center of the Establishment Dem organization.  If Clinton loses this area she is scrod.

6.  On the GOP side look for the returns from Mason City (Cerro Gordo County - IIRC,) Sioux City (Woodbury County), and Council Bluffs (Pottawattamie County.)  If Huckabee wins here he wins big.

7.  Huck-a-duck-a-bumblebee also needs to do well in the early returns.

8.  The number 3 on the GOP side should emerge early.