I just got a bulk email from the 37signals mailing list. One of their tips was:

Standardized emails are too long. These usually take the form of
"Welcome to our product" emails or verbose auto-responders that
have one line of steak and 150 lines of sizzle. People don't read
these things. They're too long, they're too wordy, they're too
fluffy.

This tip was on line 115 of a 175 line email. Nice going guys.

update: Jason Fried of 37signals and I just had a email conversation about this. I'll excerpt his very excellent point (without his permission):

Ha! We weren't talking about newsletters, we were talking about
welcome emails when you sign up for a new product.

A newsletter is something people expect to read. It's news, it's a
letter.

A welcome email for a new product isn't something people expect to
read. It's something they just "get" because they signed up for
something. It should be short and to the point.