Angela James from Carina Press posted this in response to lots of requests they'd received on the topic. I've mentioned before that you can't expect editors to give you personal feedback, mostly because of time constraints. But I'm not an editor, so it's understandable if you need to hear it from the real thing:
As an example of the time comparison of the difference between sending personal rejection letters and the form letter, I sent somewhere over 80 rejection letters on Monday. Approximately 15 of those were letters that contained personal feedback, and those letters took approximately 3 hours to send. Not because I was writing the feedback, but because I was reading through the feedback provided by the editor, taking it, editing and rewriting it and shaping it into something meant for the author of the manuscript. That didn’t even include coming up with the feedback myself!
Tellingly, she reflects my own experience reading through submissions and sometimes simply not being able to give proper feedback:
Besides the time investment, the rather hard truth is that sometimes there’s not much we can say about a manuscript that would be constructive for the author. I know that’s a difficult thing for any author to hear, but most editors and agents will tell you the same; sometimes, it would take more time and energy to craft constructive feedback than it did to realize that the manuscript was not ready for publication or not suitable for our press.
If you've ever received a form rejection and felt frustration at the lack of helpful commentary, read the rest in detail here to get a glimpse into the whirring machinery that has to process your writing: http://carinapress.com/blog/2010/02/personalized-rejections-why-not/
Also, I love this advice:
The critique partner who thinks every word you write is a special snowflake may not be the one for you, as they’re not helping you learn.