Thanks for following up on my poll. I really wanted the details on email like you mentioned but didn't want to have an outrageous number of choices. When I mentioned email I meant all of the choices you mentioned and I'm disappointed people didn't explain that part much but I'm glad people are getting into it here.
Anyway, I'll join in here. I've got 3 hosting accounts and 1Heroku app. On my shared host (mediaTemple gs) I just use their default email. For app notifications I'm using PHP's built in mail function with properly setup MX. There's no need for anything fancy on that account as its a dominantly static site that I just need to receive email from and use simple contact-form-type functions for sending mail from the site itself.
Then there's my VPS at Webbynode which I use to host multiple sites with Apache virtual hosts. I'm usually a huge control freak but decided to farm email out to Google Apps for the sites hosted on that server as they're mostly my playground/experiment projects. I'm still deciding what to use for outgoing mail from the apps on that server and for now I haven't enabled any notifications from anything hosted there.
Then there my Linode which is my baby that I care for to such a degree that I'm almost paralyzed by having to choose how to configure it perfectly. I used to have that server set up with Postfix in addition to my favorite app that I'm building there but just last night decided to remove it because of some of the comments from my earlier poll (the one that this post's OP wrote this in response to). I'm going to farm out company email because I don't want to deal with needing more memory, storage, processing power, etc. plus I'm just one man and dealing with domain keys, blacklists, and all those other delivery headaches are just too much for one person and I'd rather focus on the app itself. I'm leaning towards Google Apps for company email, Postmark for email from the app itself, plus Twilio for SMS notifications.
For all my mass emailing needs (newsletters and marketing and such) I've been using MailChimp for several months and I'm very happy with it. I use it across all my sites and apps that need it. I didn't mention my Heroku account because I don't plan to use any kind of email for that one. I may want it but there's no real justification for using it as that one is yet another playground for Ruby experiments and learning. It's hard for me to resist however because there are so soooo many new and shiny toys out these days that it's hard to focus. I've always been a strict PHP guy and now I'm off in 10 different directions with Rails, node, Python and everything else that ever gets mentioned on HN. I'm a dabbler in everything and a master of nothing (actually I'm a master of a few things but the dabbling to mastering ratio is heavily weighted toward the dabblng side).
So that's what I use and I'd also add that SaaS/PaaS and VPS/dedicated hosting is superior to other options but I still think its always good to have a spare shared hosting account lying around for times when you need to get something simple up very quickly as in just a few clicks. I love my VPSes to death but I've found myself glad to have my extra MT (gs) account on a number of occasions.