Most Liberal Senator

We've heard it stated many times during this campaign that Barack Obama has the most liberal voting record of any US Senator. This ranking was done by the National Journal.

Here are some details to provide more context:
1) The tally is for 2007; his ranking was 16th in 2005 and 10th in 2006.
2) Strange as it sounds, Barack Obama had a higher conservative score (4.5) than John McCain.
3) Three senators do not have scores for 2007 because they missed more than half of the rated votes in an issue area: John McCain, R-Ariz., who was running for president; Tim Johnson, D-S.D., who was recuperating from a brain hemorrhage and returned to work on September 5, 2007; Craig Thomas, R-Wyo., who died on June 4, 2007; and John Barrasso, R-Wyo., who was appointed to succeed Thomas on June 22, 2007.
4) Coincidentally, Sen. John Kerry was also ranked most liberal when he ran for president.

Reminder: McCain has chided Obama for voting "present" while in the Illinois State House, but has himself missed so many votes in the US Senate that his voting record could not be ranked by the National Journal.

Here are a sample of the bills that earned Senator Obama the ranking of Most Liberal:

1) Voted to establish a Senate Office of Public Integrity to handle ethics complaints against senators.
2) Voted against reapealing the federal minimum wage and giving states the authority to set minimum wages.
3) Voted for final passage of a bill implementing the 9/11 commission's homeland-security recommendations.
4) Voted to approve legislation reauthorizing and expanding the State Children's Health Insurance Program.
5) Voted to prevent Mexican Trucks from operating on most US roads.
6) Voted to require longer rest periods for US troops sent to war.

Source: National Journal's 2007 Vote Ratings.
http://www3.nationaljournal.com/voteratings/sen/lib_cons.htm?o1=lib_composite&o2=desc#results

Thoughts, reactions, reflections welcome.