In current lingo, it is called a Hashtag.
The idea is similar to "tagging" on FB, or labeling your emails - it's a way of filing something. So that either right now, or in the future you can search all of #bunkbeds and find every conversation filed under that hashtag.
In real time, it's so you can search in the twitterverse (universe of all tweets) for whomever is talking about that subject. The NASCAR race on Sunday was using it.
I've also seen news and political tweets use it in a sarcastic manner (#readmylips or #obamacare). You may also recall hearing a lot of the kids saying "winning" these days. They are copying the #winning tag that was at the end of several Charlie Sheen tweets.
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an example of its use:
smartass:
Tweet: My son ate prunes for dessert tonight. #diaperdutyforme
purposeful
Tweet: President Obama and Candidate Romney debate next month. #POTUSElection2012
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btw - when you verbalize #sillyquestion, it is spoken "Hashtag Silly Question". It's a way of showing your true feelings behind what you say, in a fun smartass kind of way. #internettourguide
:)