I recently did a guest post on the blog of Hartline Literary (called "From the Heart" - talking about "10 Smart Questions About the Query Process." You can see the entire post on the Hartline blog and see a quick excerpt below.
1. Can you re-query an agent after she rejects you?
You can, though I’d say you have about a 50/50 shot of getting your work read. Some agents seem to be more than open to reviewing a work if it’s been overhauled or undergone serious edits. Other agents, meanwhile, believe that a no is a no—period. So, in other words, you really don’t know, so you might as well just query away and hope for the best.
2. Should I mention that my work is copyrighted or has had professional editing?
No. All work is copyrighted the moment you write it down in any medium, so saying something that’s obvious only comes off as amateurish. On the same note, all work should be edited, so saying that the work is edited (even by a professional editor) also comes off as amateurish.