Steam Demo's

I have recently got back in to PC gaming, after going away and primarily using consoles and now i am back and using Steam, I was wondering: 

If I download a game demo (Game in question is Trine) and play through a load of that, when I finally purchase the full game will my demo save roll on to the full purchase or will I find myself having to restart from the beginning? 
 
Thanks in advance!

It depends on the game, but generally it's like any demo in a console. You'll have to restart from the beginning when you get the full game.

Not sure about Trine but I know when I did that with Torchlight buying the game literally was an unlock and so the save rolled over.

" Not sure about Trine but I know when I did that with Torchlight buying the game literally was an unlock and so the save rolled over. "

See that's the one I was confused with. Torchlight rolled over. I guess it's not that big a problem because I am really enjoying Trine and it's not going to take long to catch up to where I am right now. Thanks for the help!

It does depend on the game, but I'm fairly certain that my Trine demo save DID roll over when I bought it. I still have a "trine demo" folder in my steamapps folder that holds my save. 
 
 
And since Trine is on sale for $5 right now, I highly recommend it. It's worth it at that price. Once I got farther in the game, I ended up just using the Thief for everything, and that took some of the fun out of it, but it's such a beautiful game that you owe it to yourself to buy it at that price.