This is borne out by my experience. A slowly increasing number of my friends are cutting down their use, and eventually leaving. This might just be due to my cohort of friends getting older, but the article claims it is a general trend. What is definitely true, is that nobody I know feels anything positive about facebook, at all. It is seen simply as a sinister, addictive[1] necessary evil. This is the case regardles…
Twitter seems to be losing steam faster than facebook, which I think is a shame. (E.g. http://attentionmeter.com/?d1=facebook.com&d2=twitter.co... ) My experience with Twitter (which I use all the time) is that spam is getting worse and worse and Twitter isn't even doing obvious things to fight it. Facebook is simply built of spam, so that's not an awful comparison, but I think it's hurting Twitter.
It's rather easy to 'get' facebook, since it's pretty much a mish-mash of various communication technologies that have already proved themselves, including Twitter. I think new, non-techy visitors to Twitter are confused by what it does in some ways. Twitter's interface and presentation play a large role in that.
Twitter feels less personal than Facebook. The 73x73 image is tiny compared to Facebook's profile image, and there's little info on the page about real social connections. You are limited to one type of content, tiny text messages. It seems like a social site, but doesn't feel very connected. It seems to me Twitter is a mess of missed opportunities and muddled focus right now. They've tried to push it as a way to keep up with celebrities... Apple's iTunes 'ping' hasn't worked out with that whole Pro>Consumer set up.
I think Twitter's strength is in being a messaging system. People could use it to replace SMS, free, with a better interface - or does it have a better interface? Twitter's DM capabilities leave a bit to be desired. The web interface is rather feature-free, and aren't they cutting off API/OAuth access to DMs soon or something? Anyhow, look what the NYT did with Twitter's service recently - that is the sort of building on Twitter I see occurring, but I'm not even sure if Twitter themselves understand the potential for Twitter to become infrastructure, not just a way for people broadcast how much you hate traffic or like a sandwich.