Sure, if your Exchange server uses ActiveSync. However, most enterprises that use BES tied into Exchange won't feel the need to get ActiveSync set up.
Or you can get mobile.me to have Exchange, but I can't see enterprises paying for that either.
And of course, you can use Yahoo mail (even on a 1st gen iPhone) to get Push, but let's face it, who wants a yahoo address when they're trying to look serious?
So, yes, the 2.0 does Push, but you need the infrastructure. If you're working for a Blackberry-biased enterprise, you'll be hard-pressed to get Push on your iPhone.