custom – shared code for different projects ratio

Hi all, if you had a company, and you had to build different projects, would you write each one from scratch, would you re-use all your existent code base or just some part of it? All these approaches have both pro and contra. I know that the right reply is always depends.. but what do you think? I'm into the share as much as possible. More effort at the beginning, but incredible advantages with time. How about other companies? It would awesome to know the amount of shared code between different applications from the same company.. e.g. Access, Word, Excel and so on for Office, Open/FreeOffice to stay in the open source world etc.