One of the problems with SETI is we are looking at the wrong technology. Radio signals just aren't a very good way to communicate between star systems. Lasers do a much better job but you would have to be in line of sight to pick one up. Radio signals become worthless as you move light years away from an object. Layer on top of that compression and encryption technologies and you have something that just looks like noise.

My opinion is that we just don't have the technology to see them yet but are tantalizingly close. Life is rare and hasn't spread out enough. While robotic probes could spread quickly through the galaxy, it might be just too difficult to do this. My prediction is that we will see some evidence of an alien presence within about 100 years. The question is what will we do when we do find it?