Hi all.
Sorry of I have missed this somewhere else. This came up in a game recently, and was wondering if there is any clarity on it:-
Spell:- Hydraulic Push
You call forth a quick blast of water that knocks over and soaks
one creature or square. You can use this blast of water to make
a bull rush against any one creature or object. Your CMB for
this bull rush is equal to your caster level plus your Intelligence,
Wisdom, or Charisma modifier, whichever is highest. This
bull rush does not provoke an attack of opportunity. Hydraulic
push extinguishes any normal fires on a creature, object, or
in a single 5-foot square which it is targeted against. Magical
fires are unaffected.
Now... the rules for Bull Rush take account of the size of the creature doing the pushing (i.e. you can only Bull Rush a creature up to one size larger than you). 
Ok - so, we have a gnome casting Hydraulic Push (and thus trying to Bull Rush), trying to affect a Large creature. Should it work? The gnome (by herself) could not (she is classed as small). However..... what size is the spell classed as? If it is also classed as small, then it means that a given spell becomes more effective simply because the caster is larger. If cast by a human sized caster, it would work. As far as I can tell, the implication of this would be that because of your size, you could cast better spells. 
In the end, I simply declared that unless a spell specified otherwise, it should be classed as "medium" - and thus allowed the Bull's Rush attempt (besides - it was rule of cool - she was trying to push a big bad over a cliff, and it looked really good).
However - was wondering - is there anything "official" on this?
Cheers
Aiddar