I think, instead of a goo or ash pile, it should be a goo-covered or charred skeleton (with ash around it). Not sure how well that would play with dismemberment.
You know, that would be pretty nice.
Although lasers should rarely, if ever, actually burn a human sized target into ash, I would say. Rather, they should simply cut off limbs, after all, a laser is a very focused beam, and I doubt tthat even one powerful enough to be used as a weapon like in Fallout would be able to burn an entire human being's body into ash like that if it was such a small beam as we're shown in Fallout 3, the ash piles should be reserved for a different type of weapon if they're used.
I do hope that ash piles and goo piles despawn in New Vegas, though, and I really don't see how it could be that hard to do it.