Do people low on agreeableness swear more? Reading through a scientific report on Big 5 characteristics in everyday life, I found a -.28 correlation for Agreaableness and swearing.
http://dingo.sbs.arizona.edu/~mehl/eReprints/EARlensmodelJPSP.pdf

Do other studies usually support this? 
Is swearing (in combination with other cues) a useful indication of low agreeableness?
There are a number of findings showing that people who are low in agreeableness swear more often. Apologies for the long full quote, but the relevant literature has just recently been nicely reviewed in a chapter about "Natural language use as a marker of personality" by Ireland and Mehl (2014). They cite the study you based your question on (Mehl, Gosling, &amp; Pennebaker, 2006), which is very nice because it uses a relatively unobtrusive recording device (the Electronically Activated Recorder, EAR) to collect data about naturally occurring conversation. However, they also cite additional evidence that is in line with this finding: 


  Another face valid linguistic correlate of agreeableness is swearing. Unsurprisingly, people swear less to the degree that they report being more agreeable (Holtgraves, 2010; Mehl et al., 2006; Yarkoni, 2010; see Jay, 2009). 


Is swearing a reliable indicator of low agreeableness?


  Indeed, the five words that best discriminate between individuals ranking high and low in agreeableness in Facebook status updates are all swear words (Schwartz et al., 2013). The negative correlation between agreeableness and swearing fits with lay theories of personality as well and is correctly interpreted by outside observers of students’ EAR recordings (Mehl et al., 2006). Given the low overall incidence of swearing – making up about 1/3 of a percent of spoken conversation and 1/10 of a percent of emotional writing – these results essentially mean that highly agreeable people are unlikely to swear even once in a given sample, whereas a highly disagreeable person might swear only a few times. Nevertheless, swearing, like negative emotion words, another low-frequency category, is a potent and reliable indicator of agreeableness and other key psychological variables (e.g., Robbins, Focella, Kasle, Weihs, Lopez, &amp; Mehl, 2011).


References

Ireland, M. E., &amp; Mehl, M. R. (2014). Natural language use as a marker of personality. In T. M. Holtgraves &amp; T. M. (Ed) Holtgraves (Eds.), The Oxford handbook of language and social psychology., Oxford library of psychology (pp. 201–218). New York, NY, US: Oxford University Press.