Well I ran it through the ultimate Push test and it passed with flying colors.
While standing outside of my office building, I deleted my .Mac account from my iPhone (2.0), which in turn deleted every single one of my Calendar and Address Book entries (leap of faith...heh). I verified that they were gone in each app. I then added my e-mail again, this time using the MobileMe setup option on the phone, and set it to sync via Push for Mail, Contacts, and Calendars. Then I went inside and took the elevator up to my office.
Everything is back on my iPhone. All of it.