If the "urban" crosstab is to be believed, then both Carson and Trump have the potential to be screwed over by the RNC's delegate allocation, since so many states give every congressional district the same # of delegates, and there are fewer Republicans in cities than in the sticks.
Granted, Trump's current lead is big enough that he'd still win a plurality of delegates if every state voted today, but if his lead slips, this could be an issue.
Delegate election will be critical if the large field holds up through the primaries. In IL every CD elects three delegates. The top three delegates in each CD will win, and in some cases that win will go to a well known figure in the CD regardless of the person that delegate supports for president. I'm guessing most other primary states are similar.
Illinois’s delegate selection method is actually not very common at all. It’s one of the few states in which the delegates are directly elected, and their names appear on the ballot. Pennsylvania’s primary operates similarly, but the vast majority of other states determine delegate allocation based on the votes cast for the presidential candidate himself/herself, with the name of the delegates not appearing on the ballot.