Most infopath  forms usually fail on the WCAG 1.0 level of accessibility  at checkpoint 6.3 which restricts the use of scripting. 508 section  1194.22 (its comparison)
www.access-board.gov/sec508/guide/1194.22.htm#(l) is less restrictive but an equally impressive read. If you can make your form comply then well done!

On the server side, if I recall correctly forms libraries typically fail on Sect 508, 1194.22(g) Row and column headers shall be identified for data tables. If you are bypassing forms libraries and storing the generated XML from a submitted form in a DB this might be a moot concern.

The problem with saying that InfoPath is accessible or Section 508 compliant is that the accessibility  text for the text form fields are not read to JAWS version 10 or below; only JAWS 11 will read the screen tips appropriately. Therefore, to say it's technically compliant is one thing, but if the assistive technology of the audience that the InfoPath is designed for is not up to date, then it is not Section 508 compliant.