The fact that she's thinking about running doesn't really surprise anyone. It's just now that she's openly admitting it. She's moved from the, "I don't know what opportunities may come my way in the future or I'm taking time to see how I might serve the country the best way" to the, "I'm thinking about running" stage. Next is the forming an exploratory committee stage followed by the all out run for the office.
Clinton is the odds on favorite to win the Democratic nomination should she run. She also leads most of the major Republicans in the early polling when it comes to possible General Election matchups. I think she represents the Democrats' best chance to hold on to the White House.
The Republicans will have a different task. While Clinton would likely have clear sailing, there will be lots of bloodletting again on the Republican side. The GOP would be wise to rally behind an electable candidate.
There's still a long way to go until 2016, but Clinton's announcement signaled yesterday that she just may run again for the White House eight years after her first attempt.