It will be interesting to see if Facebook clones every single Google+ feature before Google+ is out of invite-only status. I'm guessing next will be a basic rich text status editor, to go along with the already announced video conferencing.
That said, I also don't think Facebook is going anywhere any time soon. But it'll certainly be interesting to see Facebook's first moves in response to G+.
Remember how Facebook was going to be a walled garden web 2.0 platform, and how Facebook then effectively killed it?
No one is forced to use any of Google's products - Bing and Facebook are only a click away.
A monopoly born from having a superior product is not the same as a monopoly gained through the practises of price fixing or forcing people to install your web-browser with no way to disable it.
I say "generally" because there are weaknesses. For instance, I don't think you can export your search history or the archive for a google group. You can export your "contacts" but not all of your social connections (at least I haven't found a way). I also haven't found a way to export saved maps or other geo data.
If they expand this policy to all (or essentially all) of your data, they are pretty much immune to anti-trust. And more importantly, it's just better for users. Google has nothing to fear giving your data back to you, anyway -- the only companies that are afraid of that are the less competent ones.