Our results show that scientists who interacted more frequently with journalists had higher h-indices, as did scientists whose work was mentioned on Twitter. Interestingly, however, our data also showed an amplification effect. Furthermore, interactions with journalists had a significantly higher impact on h-index for those scientists who were also mentioned on the micro-blogging platform than for those who were not, suggesting that social media can further amplify the impact of more traditional outlets.
via Opinion: Tweeting to the Top | The Scientist Magazine®.
I’m surprised there’s no mention of altmetrics in this piece. Results are relevant for altmetrics, though. Hoping they’ve published the study in more detail somewhere so I can check it out.
In any case, this is a quick and thought-provoking read — though it appears that it’s more about being tweeted to the top than tweeting to the top (two are interestingly related, however, I suspect).
jbrittholbrook 
Would there be reason to look for the Matthew effect here? That is, the h-index boost may be due to savvy Twitter use/spam Tweeting independent of the work.
Yes. I suspect that those active on Twitter will also receive more tweets, in general, as well as more tweets for their articles. Other studies have shown a correlation between early buzz (on Twitter) and higher citations. So, more active tweeters are, it seems, more likely to be cited more.
But it’s also the case that there might be something of a Matthew, Jr. effect. By that, I mean to suggest the possibility that younger researchers get more of a bump from Twitter, especially if you’re looking at H-indices. That’s so because younger researchers are both more active on Twitter and because they have lower H-indices (and so H-indices that may rise more easily than older researchers). In any case, I think such a Matthew, Jr. effect would be worth exploring.