One of the greatest mysteries to me is why most file managers don't have tabs - it makes performing tasks so much simpler. I've found a lightweight file manager for Ubuntu called PCMan that gives you most of the functionality from Nautilus, but also has tabs.
To install this file manager, you can either use the built-in Add/Remove applications dialog or use the command line. Just type in PCMan into the search box, and change the drop-down to "All Open Source applications" and you'll see it in the list.
Or you can much more quickly install it with apt-get:
sudo apt-get install pcmanfm
Once it's installed, you can find it under System Tools \ PCMan File Manager
And there we are… you can see that it has a decent amount of options, although not quite as many as Nautilus does.
The one option that it has by default that Nautilus doesn't have is the "Open in Terminal" option, which I find much more useful than anything in Nautilus.
Install Tabbed File Manager in Ubuntu