From an email query received today:
“Please contact me using the enclosed SASE if you are interested in my completed manuscript.”
And people think agents are kidding when they say to proofread the query letter. This is your first impression. It may be your only opportunity. Don’t be careless. It’s only one page (in most cases). If this letter isn’t important enough for careful scrutiny, what is that likely to say about the attention given to the manuscript itself?