Coming from a High-Ranking 10 man guild i had a lot of experience doing 10 man heroics. Now that i have switched to 25 man i do notice MAJOR differences.
Let's go boss by boss:
Shannox- Not a major difference, in my experience i would actually say its harder on 10 man.
Beth'tilac- Much Much harder on 25 man from a healer point of view.
Ryho- A LOT Harder on 25 man, Huge healing difference from 10 man.
Alz- [Haven't tested 25]
Bale- [Haven't tested 25]
Domo- A lot harder on 25 man heroic. In 10 man its easier for the fact that you can just rotate around the circle rather then having set spots which in turn means higher dps and less people getting hit by leap. Also in 10 you don't have to do the spread strat to kill it.
Rag- From a tank healers point of view it seemed relatively the same. Haven't tested how different it is on heroic yet for obviously reasons, but i suspect 10 man is easier if you have the right comp, seeing as how there is a lower health pool for 10 and as long as you can master phase 2 its a kill.
Drop ideas/Comments/Experiences below.