Plenty. Protip from a sysadmin in the hosting industry: don't even try to run your own MTA unless you're just curious as to how hard reliable mail delivery is.

Use GMail or similar. Use iContact / StreamSend / MailChimp for newsletters. Use Google Apps for any business you start.

Well, the (sending) MTA is not exactly mine: I configured exim to send everything through my ISP's. Of course, the domain is still managed by me, and so is reception, although I keep Google Apps (free) for the backup MX.

In my experience very low. But you should really configure your mailserver to have the advertised hostname match the reverse hostname for the IP ("PTR record")[0]. The chance of getting your mail rejected if those don't match is a lot higher.

[0]: "PTR record" is the wrong terminology for this. The *.in-addr.arpa is a special PTR record to implement a reverse host lookup. The PTR record in DNS has some other functions as well, e.g. service discovery.

As coob mentioned it could be rejected by some providers. Overall I think that situation when your emails are rejected by some providers is the worst possible. It is even worse than when all providers reject your email. For me the easiest way to track down such things is reading mta logs.

I've had a few servers reject our office mail for it when we changed IP and forgot to update the PTR