I post it anywhere and everywhere. GMail's spam filter is good enough to block 99% of junkmail, and having a single obvious address really helps when someone real's trying to contact me (eg, for a question / bug report). Additionally, I think things like "address AT YAHOO DOT COM" are stupid beyond words, and try to contact people with such addresses by alternate means (to avoid encouraging it).
Somewhat related, I see no point to using a pseudonym for most websites. Posters are often careless enough with their personal info that a clever reader can connect pseudonyms to real names. Posting under your real name eliminates this false sense of safety, and provides a mental "do I really want to be responsible for this text?" safeguard against poorly edited posts.
I picked up a trick from my friend that's been working pretty well.
I have danieljackoway.com mail setup with Google Apps, and I have it setup so that *@danieljackoway.com forwards to <my actual email>@danieljackoway.com. I generally respond from <my actual email>@danieljackoway.com, but I don't give it out online at all. (It is on my business cards, though.) My normal pattern for signing up for stuff is to signup with foo.tld@danieljackoway.com. And then if they won't stop spamming me or they leak my email to something spammy, I know who they are and I can setup a filter so I don't see any of it.
I also use it to tell where people are emailing me from, to an extent. So in my hn profile is hn@danieljackoway.com (which, if I ever get popular enough that I need to start filtering hi@danieljackoway.com to skip the inbox, I can give precedence to).
I also have a label that gets applied to things that are actually sent to <my actual email>@danieljackoway.com
I do something similar with wildcard forwarding, only instead of filtering those emails, I full out block an alias when I start getting spam there.
Though I must say that I've been surprised at how many (theoretically) legit places have leaked my email address. Like when aweber got hacked, I suddenly started getting spam on a whole bunch of aliases.
If my address gets leaked but I still want to continue getting email from a company, I update my email address with them to include the (then) current month and year (so companyMMYY@) and then I disable the old alias. So far, I haven't gotten any spam at any of these new MMYY aliases so it kinda feeds my suspicion that their mailing list must have been hacked.
An analogous trick if you don't have a domain name is to register with +identifier at the end of your email name, i.e. myname+foo.tid@gmail.com. Depending on your client, you can then see who's spamming you.
To be fair though, the spam recognition on gmail is so good that I don't even have to worry about hiding my email. I rarely see more than 1 spam email a month.
I use a pseudonym here so I can actually speak my mind. But when I openly use my True Name, my address is generally there with it. I don't obfuscate it because it seems inappropriate to deliberately break something and require correspondents to work around it just to reduce a problem that's mine, not theirs.
My mail is handled by a VPS with greylisting, with a wildcard alias. I have greylisting and stringent filtering turned on for most aliases (including my most public one, which is available all over the web) but I have an alias which is more private with no greylisting or spam filtering, which I give out to places I trust when I want a quick guaranteed reply.
If the non-spam protected alias gets leaked, I simply change it - and it continues to work, with less spam protection.
When dealing with sites I don't trust much, I instead make up an alias specific for that site so I'll know to trust them even less if I get spam to that alias.
I've had the same main email address for over 15 years. Back then, there was no spam. I can recall my extreme annoyance when spam started ramping up in the late 90s. Eventually, I installed a fantastic challenge-response system called Active Spam Killer. This program cut my incoming spam levels from around 600 per day to close to zero. Some spammers have figured out ways to get around it, but my Eudora filters get most of the rest of it.
I use gmail, mostly, and use the +identifier trick if I'm giving my email out to shady websites. Honestly, though, the spam filters in gmail are good enough that I don't worry about throwing my email out wherever, and if anything gets through I can either set up a filter or mark it as spam for the future.
I am worried about the +identifier though because it is too easy to identify what the real address is. Hotmail apprently allows you to create random email addresses on the fly. That should help you keep your email address private if you wish.
I have 3 emails. A personal one, one I use for social networking, and a business one. The passwords to each are different and so far, I haven't had any spam problems or anyone emailing me who I didn't want. Maybe it's just me, but I think I have a good stagey.
Somewhat related, I see no point to using a pseudonym for most websites. Posters are often careless enough with their personal info that a clever reader can connect pseudonyms to real names. Posting under your real name eliminates this false sense of safety, and provides a mental "do I really want to be responsible for this text?" safeguard against poorly edited posts.