Portugal to join Spain?

I've just had lunch with a couple of friends, and one of them mentioned that Portugal was thinking about joining Spain...
Now I was wondering if anyone had more insights into that matter. Is it just a rumour? Are there actually plans of uniting the two countries?
What would be the benefits, what the drawbacks?

I can't see it happening, I've "only" lived in Madrid for 3 years, but still don't see the countries as close.. I mean, just because they're neighbours it doesn't mean they have to unite. (USA <-> Canada).