edit: oops I didn't see the recent post below me b4 I wrote this

I guess my main point was to not let one's self be defined by their illness... the word choice probably doesn't matter much in the end.

The way I think about it is that you'd say bipolar disorder just like you'd say diabetes.

Then "I am diabetes" would be like saying "I am bipolar disorder" or, more briefly, "I am bipolar."

So I have the personal preference of saying "I have bipolar" instead of "I am bipolar" but that's just me. I don't have anything against the "am" word choice per se.