I try to use open source software and open standards as much as I can. I try to persuade others to do likewise, but I end up using various proprietary systems anyway. I think that nearly all of those are so that I can participate in social networks.
I use Skype to communicate with family and colleagues because it has become the default for VOIP. I know there are open VOIP platforms, but I don't have time to support family in setting them up and my work colleagues are unlikely to change.
Can we expect sites like last.fm to go open source? Others, such as Facebook, are even less likely to as it would enable others to compete on features.
This post was inspired by this article about using identi.ca rather than Twitter. The quote from ESR is choice. I'm on both because some people I want to follow are only on Twitter. identi.ca only has a small fraction of the Twitter user base. That doesn't stop me having some great discussions there. I'd love to drop Twitter, but don't want to lose that part of my social network. So practicality triumphs over principle again.