I consider myself recovered from BPD traits. I still have recurrent depression, but my last three relapses have each been shorter and less severe than the previous one, thanks to the tools and insights I'm gaining in therapy. I'm definitely learning and growing. As far as my depression is concerned, I find it helpful to view recovery as a spiral staircase - in one sense I'm going round and round (relapse and recovery), but in another I'm moving closer to the top with every circuit.
I don't think my BPD traits were ever part of my personality... with the exception of the lack of sense of identity. They were ways of coping I used in desperation. Now that I've learned healthier ways of coping, it's like the weedy and overgrown road Jim described - why would I want to go back on that road when this one's so much better? It does take a lot of time and persistence to get to that place, where the new coping mechanisms are more familiar than the old, but it can be done.

I do think I have personality traits that made me more prone to BPD, and those are still there, and probably always will be. For example, I'm naturally quite an emotional person, and if I do something, I give it my all. But in themselves, those traits aren't a problem, and I don't consider them a disorder. It was only when they were combined with a childhood I hadn't come to terms with yet, and not knowing how to cope healthily, that they made me ill. As far as finding a sense of identity is concerned, I think that was partly caused by living such a chaotic life (because of the poor coping mechanisms) and partly that I hadn't really grown up yet. Finding my sense of identity hasn't changed "who I am", I've simply grown up like any other teenager... just a few years later.

I realise this may be different for me than for someone with full blown, diagnosed BPD. It will probably be different for people who meet different BPD criteria, as well. I think some of the criteria seem to be more about personality than others. But I do believe personality evolves and grows slowly over time with life experiences, and therapy can facilitate that process.