I offered advice prior to OCI, and now I am offering advice in relation to mass mailing... Feel free to PM me for more individualized questions.
If you are going to mass mail:
1) It is not too late
2) Create cover letters and put them on the main body of the e-mail.
3) Create narratives. For example, have a format for NYC Corporate firms (I did this prior to law school, am doing this now, I want to be in NYC bcz of this).
4) Use 3-4 different formats, and then just change firm names/recruiting contact info (found on NALP). For example, have a home-market, litigation cover letter. Then have a home-market, corporate cover letter. Have a region you went to school cover letter. Have a NYC cover letter. Have a practice area cover letter (all I want to do is Tax, or bankruptcy, or employment, and you guys are the best at it and I have already done this--use chambers to find area specific firms) Having such formats can save you a ton of time, while at the same time it makes you sound as if you are sending a personalized e-mail.
Good luck to you all; if OCI did not work out it does not mean that you are out of an SA position if you are not complacent.