Also, use mod_perl if you possibly can.

There are some suggestions about sending mail from mod_perl here. These apply for CGI scripts too. The key idea is to queue the mail and not make the user wait for it. You can do this easilly with qmail-inject if you run qmail, and there are similar ideas for other mail programs.

Also, archiving while your user sites at the other end of the connection is definitely bad. Under mod_perl, you can put things like that in a post_connection handler. With CGI, it's trickier. You have to fork. This column by merlyn shows how to do it.