chrisn-585491 (8/12/2013)
1. community editions may be free and will get you started but once you get beyond a certain point you will want the commercial editions which are definitely NOT free.
This is not true of most OSS software. However if you get over your head you can hire professionals to help. (Just like the commercial software world!)
2. If you need support then this is NOT free. In fact "professional services" can be very expensive.
This is true of all software commercial or OSS. Or medical or legal services.
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chrisn-585491, very true, and good arguments.
David, I think you have some good reasons to be concerned, but a lot of them aren't necessarily different with commercial software. SQL Server has tended to not require as much in terms of professional services, but I'd bet that PostgreSQL doesn't either, if you are using it as a database as most people do. If you push the limits of the platform, sure, but in either case (MSSQL or PostgreSQL), you'll be paying for help.
Note that I didn't discount staffing costs. Moving to PostgreSQL (or any other platform), doesn't mean things are cheap and free. But it means that your cost for a developer year of time on an 8 core machine is $103,000. $100,000 for the developer (round numbers) and $3k for hardware. With licensing, that could be $120k for standard or $160k.
The difference goes down with more developers, but it's not always insignificant. The tradeoff is if your developers don't spend more time with an OSS platform than they do with MSSQL. On a single app/instance, it might not be simple. If you have 10-20 instances for various apps, the difference could be dramatic, if you have good developers/administrators.
There's no clear answer. However I'd consider other platforms, especially as tools mature that make it easy to write for multiple platform from more languages and IDEs.