I have no other bidding system experience to compare ClassBid to, but in my opinion it is very good at selecting your priorities. Gathering from what others at JetBlue say (those with other bidding system knowledge), CB is a fair system.
That being said, you have to understand that the system will give you what you ask for--if you can hold it seniority wise--so you must bid carefully. Our scheduling committee has issued several bidding tutorials in an effort to educate the masses on exactly how to work the system.
I have no problem flying with someone new every trip--the flexibility to make my schedule work for my particular needs overrides any desire to fly with the same crew.
The order in which you bid (Global requests, Prefer Off, Avoid, Award, etc..) is critical; the system is designed to work with your priorities established in a certain order on the bid sheet. If you divert from the established order, you risk getting something you didn't want.
I think Northwest has a slightly different system in that they can enter many variations of their request and then place a "Clear Sched and Restart" order on each, effectively making the computer start all over if their earlier request was not honored. We at JB can only use one Clear and restart request. There may be other differences as well.
In short--it is a great system with trememdous flexibility and options, but as with any system, it takes a while to learn the subtleties.