Here's a brief article on the importance of Open Standards, which, as the author rightly argues, is oribably the single most important consideration in technology today. Regardless of how superior some may feel open source software may be to proprietary software (and all readers of this site know that I feel that way myself), interoperability across all applications and platforms is the true holy grail of any project. Otherwise, you're simply limiting yourself, your application, and your customers.
Do read this article. Very important stuff.