Maybe a bit late to resurrect this old thread , but here's my twopenn'orth.
I worked with commercial, proprietary software written for only one purpose - making money. That's ok as long as the customers understand that they have a purely business relationship and that the software supplier will do everything it can to bleed them dry. Every enhancement, and customisation must be preceded by a financial negotiation, or must be looked on by the supplier as something they must provide in order to remain competitive.
I've also been a user of freeware and open source software and, generally, found it to be written by people who (as far as I can tell) appear to want to write software because they want it to do the very best it can with the hardware an operating systems available.
Given the choice I'd almost certainly choose open source over commercial. Even if I was running a business I'd gravitate towards open source - but I'd want to be sure my choice, if it is mission critical, is from an established and reputable author/team, has a sensible development plan that will keep it growing in the right direction for my business, and that priority support is also available should I run into a serious problem.
There's always exceptions to the general rules. There is masses of rubbish written by wannabe software developers of both types. Care in selection should weed that out. When you're choosing software - especially if you're going to need to communicate with the developers to request customisation or enhancements - you may be entering into a long term relationship. If you're taking on open source software, of course, you could choose to modify it yourself if you have the skills. Strictly, though, you would probably have to make your own work available as open source software so building your own propriety or trade secrets into it may be inadvisable.