Clash in Limited
Well I'm not sure that there will a standard "competitive clash deck" but I'm sold on the mechanic as an intriguing one. Its impact on the limited environment is a huge one. In a typical game this weekend players clashed 4-5 times giving each player the option of seeing 4-5 more cards per game than they would have otherwise. That is 10%+ of your cards in a limited deck exposed when they wouldn't other be.
These extra cards smoothed mana draws on a day when many players started the day playing tribes spread across three colors. Clash also dug deeper into decks unearthing planeswalkers and greater elementals across tables all day long. In sealed this gave the impression of the format being even "bombier" than others, since the chances of an otherwise weaker deck finding its board sweeping bomb was even greater.
However in Draft it seemed to have the opposite affect: pushing the most synergistic and interactive decks to the top of the tables. It is possible that as players learned the format and cards over the course of the day they were able to take better advantage of the set's interactivity. None the less I believe Clash had a very substantial impact on the way this limited format played out.
All in all, at the start of the day, players were moaning and groaning about more luck being added to the equation with the advent of Clash. Yet, I went away convinced that the randomness Clash inserts in terms of individual card effects is at least counterbalanced, and possibly far outweighed by the "chance" it removes in the form of giving both players greater card selection for a nominal price.
A Little on Colors vs. Tribes
Oh the temptation. The temptation to play more than two colors in limited is always strong and this formats temps you down the three color road as well. It is easy to fall into two colors and two tribes, and then begin bleeding into the third color of your tribes' affiliation. This is fine as a draft strategy, but as a deckbuilding strategy you can get into trouble (despite Clash smoothing) if you run more than a splash. The winning strategy on prerelease day seemed be to settle into a tribe and then add then best cards from the 1-2 other tribes that overlap your colors.