Kevin Drum does a nice job of summarizing the analysis of Bush's payroll/service records done by Paul Lukasiak.
In short, it sure looks like Bush went AWOL for 5 months, NEVER made up the lost service time, yet somehow managed to be gain an honorable discharge:
http://www.washingtonmonthly.com/archives/individual/2004_08/004454.php
If the Swift Boat Slanderers want to talk about the candidates' military service, I say, BRING IT ON!