One thing people are missing is just how corrupt the electoral process has historically been in this deep south Texas counties.  Just read Caro's biography of Johnson.  Electoral politics in these counties has had more in common with neighboring Mexico than with the rest of the US.

When Webb County doesn't release even its early voting (!) returns untill all the other counties has reported, than reports a Cuellar margin just large enough for him to win, its pretty obvious what is going on.  This has been SOP for political machines engaged in ballot tampering since the founding of the republic (and not just in south Texas!).  And this happened in 2004, too.  You think people would have been prepared.

Yes, Cueller improved his percentages in some of the sparesly populated counties south of San Antonio, but if this had made the difference, we would have seen the Webb County results alot earlier.

Also, there was a legitimate reason for voters in Webb and Zapata to vote for Cuellar, to make sure they had representation in Congress.  This area should have its own Congressional district.  Delay deliberately created two CDs stretching from the Rio Grande to Austin, and to San Antonio, with the population slightly weighted to the Rio Grande Valley, in the expectation that Valley voters would throw out liberal incumbent Congressmen from San Antonio and Austin, and put in Valley politicians, who tend to be conservative even though nominally Democratic.  These voters can't really be represented from San Antonio or Austin.

Finally, everyone forgets that Bush carried this district.  Yes, everyone there is a Democrat, but its like a cotten belt district, a majority will register Democrat but hold very conservative beliefs.

In short, this district is so unusual that I don't think you can draw any lessons from it.  I think influencing an election here was too ambitious a project for the netroots to pull off at this stage.