Demos make a difference?

[Kantor]

Absolutely.

I was sold on The Force Unleashed after the demo

Ninja Gaiden Sigma's demo, and ridiculously high review scores, convinced me to buy the game (something I've always regretted)

I was going to get BioShock anyway, but the demo was so incredible that I had to buy it immediately.

Conversely:

The Enslaved demo left a bitter taste in my mouth, and I was expecting it to be brilliant.

The Mafia II demo convinced me to never buy it (I was considering doing so when it was cheap)

So yes, demos have made quite a difference for me.