On the UCOP site, there is a page that shows you credit equivalency.
You get 20 units for getting 30pts/+ on your diploma.
As for using it to get out of courses, your SLs will be useless
Hl scores less than 5 get squat
Bio HL gets you the same thing as Bio AP (Bio 1A+B)
Math HL gets you squat
English A1 HL is the only useful one, it gets you out of R&C
Here is a pdf i found a long time ago
http://www.geocities.com/superiorhominid/IB1104.pdf