Hi Jennifer,
I think many people feel Twitter is a social network only to be used for personal reasons. However, I would challenge this idea. Twitter has many professional development benefits. For instance, following experts allows one to build what is known as a PLN (Personal Learning Network). Learning from the content that other experts are producing and sharing allows an individual to engage in informal learning about topics of interest. Given the fact that recruiters use Twitter to recruit and companies use Twitter for branding, customer engagement, and to attract talent, Twitter has yet another professional use of engaging with, learning about, and connecting with companies/recruiters. A third example would be the opportunity to network with others in industries of interest which can lead to informational interviews, job opportunities, and more. The platform doesn't determine career benefits - the user is responsible for this. If those facts are not compelling enough to reconsider the position that Twitter should or can't be used as part of one's career marketing or professional development goals, I encourage you to take a look at this exceptionally creative way Twitter was used by a job seeker to brand and market themselves and ultimately land a job: http://vimeo.com/25812909.
Robert Starks Jr.