Q:

Is a good idea to use a reset stylesheet in a started project?

I'm working in a long started web project that not use a reset stylesheet. 
It will be a good idea to include a reset stylesheet given all the things already done?

A:

If the project already works fine, and renders properly in all major browsers, don't worry about a reset sheet. For future case, use reset sheets to quickly set aside browser-differences, and allow yourself to focus on more important things.
Contrary to what others here have mentioned, don't ever use * {margin:0;padding:0}. Instead, I would suggest using Eric Meyers' Reset Stylesheet. It's well-respected by the community of professionals, and has even found itself included in some of the most used css-frameworks.

