Good points. I have a gmail account only as a backup when for some reason my own domain / email server is down.

I also use it as a "dummy" account. If I'm not sure if the site is legit. I give my gmail account. I can always change it later. Even on my own domain, I use one particular email alias as check. I give it out seldomly. Then if I start getting a bunch of spam on that account, I know who sold me.