I love Perpetual Plum! Its a nice subtle color thats close to my own & its perfect for daytime/office use, has a nice feel to it, very pigmented and has a light citrusy scent which I like :) It also sort of moisturises your lips without feeling sticky.
As for drawbacks, I would say its more of a deep reddish pink than a purple though - so not sure it qualifies as "plum". It also is not as shiny as your traditional lip gloss - I would agree with the other reviewer who described it as a "liquid lip color". As I'm not into the highly-glossed look, this is fine by me.
Staying power? I'm not sure.. it definitely doesn't survive a full meal. I guess I'm still on the hunt for a lip color that does. But I do like everything else about it. Got it on sale a few months back and immediately bought one for my sister as well. Now, its on sale again and so I got my second tube as a backup :)