Earlier quoted context omitted.
I use DKIM and have Reverse DNS + SPF and gmail likes my email just fine. However, previous to setting all that up gmail would commonly mark my messages as spam. I haven't tested it in the last few days.
And the moment someone accidentally clicks the SPAM button you'll find yourself with weeks of pain on a low volume mail server. Because, as an individual, you won't qualify for their FBL service and "mysteriously" you'll have weeks of everyone saying you end up in their spam folder.
This was years ago but I guess that person was not alone.