As a gimmick or a novelty once or twice, I don’t really see the harm in it. It is a system that is based on a lot of client trust though, and I do hope that artists provide some kind of safety net so they’re not being humiliated when they accept $5 in exchange for a decent quality image.
I do think it’s problematic if its something the artist uses constantly, though (unless their clients are so good that they’re being paid a comfortable, reasonable rate). I feel clients already have too much power over what artists charge for their work, and I’d be hesitant to give them yet another chance to undermine and undervalue the work of artists. I … sometimes get the feeling that clients think they are doing us a favour, and while all artists should be grateful for the business they receive, oftentimes it feels like we are begging for donations, it makes me uncomfortable that sometimes we might be seen as something akin to buskers on the street.
Additionally, I cannot think of one other commodity or service that relies on a ‘pay what you want’ kind of system. I think that for art and creative work to be taken seriously as a real job, then we should start implementing standards that parallel a real job, and doing away with ones that contribute to undervaluing what we do, regardless whether we are professional or amateur artists.