From experience, I'd not recommend postgres especially for larger dbs. it's good for small databases, and fairly efficient, but I worked on a gov't project where the database was about 22 Gigs, and postgres was Extremely Extremely slow. Free yes, efficient no. They waited a year, but when the next fiscal budget came out, they upgraded to Oracle on Solaris and have never looked back.
Completely agree that for large projects, Oracle is the way to go. Platform independent is a big feature. ON a project now with MS-SQL Dbs ranging in size from 12-40 GB and the quad server is overloaded. Currently it's a IT problem, not db, because we need more hardware to separate out the load. But the employer mentioned above, ended up with their multiple Oracle Databases much larger then my current project running on a single monster SUN Box, and have still yet to come close to maxing it out. Apples and oranges I know.