I recommend the detailed write-up by the Seattle Trademark Lawyer here.  He also attended the oral arguments and blogged his reaction to those arguments here.  Given the detailed write-up by Mr. Atkins I won't say much -- I recommend reading his posts on the topic.  That said, here are my quick thoughts:

What was the dispute about?  Hormel, the makers of Spam (luncheon meat), brought a "cancellation" action, which sought the PTO to cancel the "Spam Arrest" mark issued to Spam Arrest, the maker of a popular spam filtering software.  Hormel argued that it had a famous mark and use of the mark "spam" by a third party (including use in a good with a potentially negative connotation) injured Hormel's spam mark.  The TTAB disagreed, finding that the term spam had become generic with respect to email (it is commonly used to refer to email).  The TTAB also rejected Hormel's position that use of the term spam to describe email was appropriate, while use in a mark was not.

What will be the overall effect of the dispute?  The dispute clears the way for third parties to use the term spam as incorporated in a trademark for a good or service relating to unsolicited email.  Reading between the lines, my impression was that the TTAB thought that the time for Hormel to act was about 10 years ago, around the time the word "spam" was set to be inducted in the dictionary as a word used to refer to unwanted commercial email.  Once the word fell into common usage, it was probably too late.  At the least, Hormel was facing an uphill battle on this score. 

You can access the pleadings and case documents online at the TTAB's website here. If that link does not resolve, go to TTABVUE, type in "Spam Arrest" and you should see the cancellation proceeding (no. 92042134).