I have seen this type of situation all the time. Like other people already said, there wasn't enough buyers and sellers. Whenever there isn't enough buyers or sellers, everyone want to sell or buy at their best price. Therefore, if you want to buy at the OFFER price, you get it instantly ! If you want to sell at the BID price, you get it sold instantly too.
Here is an example of an actual trade that I made on May 8 (you can lookup in my profile if you wan to):
I bought +WWRAF (WFC Jan 2010 30 CALL) in the morning at the OFFER price of $4.50. Because I was willing to buy at the offering price, I got it instantly without any problem. Around noon, WFC went up and the Bid price for +WWRAF went up to $4.6 and the Offer price went up to $4.8, so I sold my +WWRAF option at $4.6 instantly without any problem. Because there wasn't any buyer, selling it at $4.7 or higher was impossible. Now, I wish that I have held on to +WWRAF until this morning because its BID price went up to 4.8 and the OFFER price went up to 5.