With several of the companies, I managed to (via either vowing silence to recruiters, or having an inside guy) get feedback on my projects. Nobody volunteered feedback willingly. And honestly, based on what feedback I did get, I see why they didn't want to offer it. It was an unscientific mess.
Generally:
* There was either no rubric or very basic rubric for scoring the assignment * reviewer gut feel and comments were seemingly more important than the score (if present) anyway * frequently, reviewers disagreed over whether a cool doodad was indeed cool or over/under engineered. * frequently, there were "gotchas" where they were either expecting you to notice an "issue" with the prompt, or they gave a vague prompt and wanted you to fish around to discover specific non-obvious things they wanted to see.
Now obviously, it's not like any strategy for interviewing software people is all that great. But at least interviews take nearly an order of magnitude less time than projects, and also have some built-in feedback via facial/verbal cues and such. Instead of just shooting your project tarball into the abyss just to get a boolean back.