It's important to know that even Jesus taught eternal punishment. He taught a lot about what it will be like. In the description in Revelation there is something that is important that often get missed.
And I saw the dead, both great and small, standing in front of the throne. Books were opened; and another book was opened, the Book of Life; and the dead were judged from what was written in the books, according to what they had done.The sea gave up the dead in it; and Death and Sh’ol gave up the dead in them; and they were judged, each according to what he had done. - Revelation 20:12-13
http://www.biblegateway.com/passage/?search=Revelation20:12-13&version=CJB
Please note that people are judged by what was written in the books according to what they had done. It appears that not everyone is judged the same. Yes they are all cast into the Lake if Fire, but the judgment is based on their deeds. So God remains just. A serial killer will be judged by his deeds and the stay at home mom who tried to live a good life and died of cancer will not be judged the same. She rejected Christ so will still be cast into the Lake of Fire but her punishment won't be the same. Just as the believers rewards are not all the same. Yes we all will be in heaven, but our rewards there are also based on our deeds. I think it makes perfect sense.
And the eternity of it all is described in Revelation as well.
“Pay attention!” [says Yeshua,] “I am coming soon, and my rewards are with me to give to each person according to what he has done.I am the ‘A’ and the ‘Z,’ the First and the Last, the Beginning and the End.”How blessed are those who wash their robes, so that they have the right to eat from the Tree of Life and go through the gates into the city!Outside are the homosexuals, those involved with the occult and with drugs, the sexually immoral, murderers, idol-worshippers, and everyone who loves and practices falsehood. - Revelation 22:12-15
http://www.biblegateway.com/passage/?search=Revelation22:12-15&version=CJB
The city is eternal and outside the city are those that are sinners. They would be eternal too as they remain outside. I think that is part of the punishment. To see where you could be as opposed to where you are. I think this fits with Jesus talking about the rich man in hell wanting Lazarus to bring him water. It appears he can see where Lazarus and Abraham are and can speak to them. Eternal separation will be its own kind of torment.
But God is loving enough not to force people to be with him if they didn't want to be there.