On Athletes and Twitter:

Since the beginning of time when cave-people worshipped the caveman who could bring back the biggest mammoth, people have always found fellow peers to look up to.  Connecting with that, one of the greatest joys of life is when someone you idolize and look up to gives you their acknowledgement, with showing off their private side being secondary.
With Twitter, fans have been given an opportunity to connect with their favorite athletes like never before, and some of the athletes have responded in kind by creating accounts that show off their more personal side that the media doesn't show.  Twitter gave fans and athletes a chance to basically interact on a one-on-one basis thanks to being able to tweet to and in certain cases, directly message them.  With the unfiltered interaction though, comes a double-edged sword.  Since athletes on Twitter don't always have a PR or marketing team helping them out, they may end up expressing their thoughts in a way that is too controversial to the general public, or just releasing information that is TMI.
Twitter is also feared as a distraction for athletes by coaches and leagues, and many of them have instituted rules banning social media during certain times to make sure their players are fully in game mode, as well as making sure they're not accidentally tweeting out the game's strategy.  One specific incident that led to this ban was the actions of NHL enforcer Paul Bisonette (@BizNasty), who regularly tweeted with fans during the game, which the NHL heavily frowned upon before formally banning the practice, since social media interactions could be seen as something that is damaging to the game's integrity.
All in all, Twitter is a great resource for athletes and fans to interact, but care must be taken so that what the athlete says doesn't end up coming back to bite them in the ass.  Social media, after all, is a double-edged sword.