Most Nerve-Racking Part of Web Design

So what’s yours?
Mine’s gotta be sending out mass e-mails for mailing lists.
Worrying about it turning out ok (espesh with HTML ones) and that the server won’t just timeout on me!

I always end up checking over my code for it a million times too.

Funny/horrifying story:
I had sent out a newsletter to about 4000 people on the Incognito website and had just kept a copy of the PHP file on my desktop. A few days later, I wanted to send one out to all the people in another site/database. Of course I forgot to change the database details and the artist ended up getting hundreds of e-mails from confused people on the Incognito mailing list! I nearly died! Ended up telling my boss that the site had been hacked!