DS got a DOCband at 9 months.  We decided to do it for a few reasons:

1)  we had tried encouraging to turn his head to the other side, but he refused.  he also had PT to fix the torticollis that was making him favor the right side.  torticollis fixed, but he still favored the right.  we thought it might even out once he was holding his head up and sitting up - NOPE!

2)  his plagio was diagnosed as moderat-to-severe

3)  his face was asymmetrical, which can cause problems in the future with jaw alignment, vision, etc.

4)  his plagio was noticeable (even with his significant amount of hair) and we didn't want him to feel self conscious as he gets older.  if he ever asked us if something could have been done, and we answered "yes, but we didn't try", we would have a hard time dealing with that.

DS's head isn't perfect and it may never be, but there is a significant change in the shape.  The earlier you get it done, the better the results.  He adjusted fine to the helmet and it was kind of cute on him.  I have no regrets.  We were able to get insurance most of the helmet.  It took about 4 months and my DH's HR department getting involved, but I believe we got it covered under the "durable equipment" allowance.  Also, there is a plagio group on Yahoo that provides lots of info and you can ask others about their experiences.

Our son also had a DOC band.  His went on at 6 months.

Our reasons are about the same as PP.  DS had slight torticollis, and the PT did not help him change his preference for facing right.  His plagio was moderate, and very noticeable in his face and ears.  We could only see one ear if he was facing forward and his right eye appeared signifcantly smaller.

Insurace did cover our band, but when we were still arguing with the ins. company for approval (that was fun), we did make the decision to go through with the band whether it was covered or not.  I too have no regrets. 

I analogize it to braces--if my parents had not invested in my braces, which was pretty much for cosmetic reasons, I would have had one terrible looking set of teeth.  I did not want DS to have to grow up with a flat head if he did not have to do so.  His head is close to perfectly round (since he still has no hair, it's pretty easy to see) but he still has a little bit of facial asymmetry--I don't think anyone but me would even notice.   

And I agree about the yahoo group--it is really helpful.   

We did the DOC Band at 4 months for plagiocephaly and could not be happier! It took no time for him to adjust and he was so darn cute with his band on! Our son's head was labeled as severe and it was very noticable. Our insurance would not cover it and 6 months later we are still fighting it (and ready to throw the towel in). DS's head grew very quickly and an estimated 12 week treatment ended up taking only 6 weeks. After seeing the pictures taken by Cranial Tech, I realized it was not only the back of his head that was affected. His ears were not aligned and his forehead was sloped. I too had the "upper hand" mentality and I didn't want my son staring off like this. Ultimately, when I considered things I had done for myself for cosmetic reasons (Invisalign), I couldn't deny my son if we were in a position to correct it.