Demos are like stock to games; if a poor demo is released then the stock (hype) of the game goes down, if a good demo is released then more hype goes toward the game.

I recently downloaded 3 demos on my ps3: haze, bourne conspiracy, and dbz burst limit. Since the first time that i heard of any of the games, i would say that i was 100% sure that i was going to get haze, waiting for more details on bourne conspiracy, and probably not even thinking about buying or renting dbz. But after i played the demos i would say that i am 100% sure i am getting bourne conspiracy, probably buy dbz used down the road, and now i am unsure if i even want to get haze. Don't get me wrong, i want to see the game do good but it wasn't that fun to me. I'll probably just get it for the online play. 

So does anyone else feel like a demo is very important or do you already have your mind set and will get the game no matter what?  Or are there many more things that you consider when debating if you are gonna get a game or not? if so what?

Demos are very important. They are snapshots of the game. They have in the past encouraged me and discouraged me from getting certain games. Obviously there are additional factors to a purchase, but if the demo is shit i cant see why i would want the game.

so are demos the most important thing in your decision?
I would say in my opinion, the demo would be the most important followed by the description of the game and finally i would read some reviews about it.

I do feel they are quite important, but I am not going to not get a game if it does not have a demo. Personally, I though the Bourne Conspiracy was not a particually good game. There were some great moments, but it was just too cinematic for me. Having the control taken away from me every few seconds was really annoying, and I was not very impressed by shooting in the second level
Overall, demos can change my opinion of games, but in some cases, they are no very representitive of whole game, like Haze, where it does not show half the gameplay or the story aspects.

Demos definetly influence me. I mean it's a chance to play a small part of the game. You get a general feel for gameplay, atmosphere, graphics etc. The best example I can think of is Bioshock. For some reason I just didn't give a damn about that game at all, I just couldn't get hyped. However I tried the demo out and loved it so much I spent the next few weeks dying to get the full game.

I think Demo's are most influential for the games that end up getting review scores of around 70% though. If im kinda interested in a game but it's only getting 70% in reviews it's usually a toss up if I get it or not. However if it's got a good demo that usually swings it for me.