Is Opera Web Browser going to be offered via Ubuntu Software Center?
Opera used to be available in the Canonical partner repository (software in the partner repository is available in the Software Centre), but it was removed in December 2008 (the version in the repository at the time was very out of date).
My analysis of this is that there is not a huge desire in the Ubuntu community for Opera, but if either Canonical or Opera had a strong desire to have it there, then it certainly could happen again.
Just download the debian package file from Opera web site and double click it to install. Once you install the deb, it will add the opera repositories to your Software Sources.
I would recommend version 11.0 beta, which has support for extensions and tab stacking, among other things.
You can add Opera's package source to Apt:
echo "deb http://deb.opera.com/opera/ stable non-free" | sudo tee -a /etc/apt/sources.list.d/opera-stable.list
You'll also need to get their signing key, else you'll get the scary "unsigned package" warning:
wget -O - http://deb.opera.com/archive.key | sudo apt-key add -
Update the package list, and then you can install it like any other app:
sudo apt-get update sudo apt-get install opera