Joel's warning is nothing to do with down-votes, but typically for abusive behaviour; most users are very friendly and will never need to know any of this, as they'll never see any of it.
This mainly applies to obnoxious behaviour; blatantly insulting other users, etc. Isolated incidents from an otherwise friendly user will usually just be removed (i.e. your post / comment will be removed or edited) - but if you are repeatedly going out of your way to be unpleasant, you'll probably get an e-mail from an ♦ admin, asking you to desist that behaviour. If you ignore the warning, your account will be suspended for an interval, most likely a week.
After that time, you are welcome back, but repeat abuses will be treated with less patience - either a longer suspension, or deletion etc.
separately to this, individual users (everyone with a nominal amount of rep) have the ability to flag posts as offensive / spam; if you get enough votes the post is automatically deleted and you get hit with a 100 point fine for your trouble (assuming the post isn't already deleted by an ♦ admin by that point - we do monitor the flags etc).
Finally - the reality is that moderation takes time and effort; if you post abuse from a new account (1 day old, 1 rep, no contribution to the site etc) then being realistic you're going to see a lot less red-tape; if your first post to the site is "you suck", then I wouldn't expect that account to survive for long, and I wouldn't bet on getting an e-mail. In particular, spam accounts are deleted on sight.