I think fewer people are worried about their mail server being hacked as they are about Google deciding on their own initiative to release info willy-nilly, as they did with Buzz.

Absolutely, I use Google for pretty much everything and trust them implicitly. I don't believe that Google will leak anything that matters and think that the whole buzz furore is nonsense whipped up by people who had assumed privacy where there was little reasonable expectation of it.

However, if, like the OP, you do not trust a major corporation with a near-immaculate record on data integrity and an industry-leading stance on LEA disclosure, why trust any corporation?

Hosting your own server is inherently risky, but it is a different sort of risk with different mitigations. As you allude to in your post, the question is whether you fear malicious individuals, the workings of the state or corporate incompetence.

your contact list doesn't matter? it was leaked via buzz.

What exactly is the danger of people having my email address(substitute me with you if it helps)?

my contact list was not leaked. i think at most the list of people you were auto-following was made public if/when you created a public profile and did not set this information to private

Google's server may be 10 times more secure, but it's probably targeted about 10000 times as much as my own server.

Well even in that case attackers won't touch your data (since you aren't targeted), so you'll be still safe. If they are targeting you then it's the same thing.

In addition, I know of no company who provides better spam and malware filtering.

Postini did, but they were bought out by google :)