New Diffusers, there will be at least one new one, Force India or BMW Sauber will be my bet.
Brawns advantage, isnt that great in Quali now, Toyota will be definately in there, ill say that Brawn have the advantage in race trim, Toyota and Williams are starting to get closer tho, Red Bull are always close to theese guys, so are best of the rest.
McLaren will take part in China and Bahrain, but i can see them getting a 5 race suspension as a team from Barcelona tho, as they will loose television revenue and posibly sponsorship money from those races.
As for Piquet, i can see him getting replaced arround the middle of the season, posibly as early as Silverstone or Germany. However, i dont see that being the only replacement for this season, i can see at least 3 or 5 mid season replacements, i can see theese:
Renault: Nelson Piquet OUT - Romain Grosjean IN (Piquet being sacked for performance, Grosjean coming from GP2)
STR: Sebastian Bourdais OUT - Nelson Piquet IN (Bourdais quitting F1 for ALMS with Peugoet, with STR needing a replacement quick, them chooseing Piquet)
Those are 2 i can definately see. I can see others involving Fisi, Nakajima and Kimi as well. But a couple of them may be announcing their retirements, Nakajima could be replaced by Kobayashi as the "Toyota Hire Driver" there as Nkajima will show he is still a moving chicane and incedent prone driver. (wishing i chose Glock now over Nakajima in my F1 fantasy team as a side note there)