I notice you are featuring a link about Elderhostel discounts on the front page on IT right now. I heartily endorse their vacation packages. I have taken 3 overseas packages with them.
The first was a two week package in Russia focussed on the arts. We went only to Moscow and St. Petersburg and the palaces outside Petersburg. We did not run around all over (which I hate because packing and unpacking gets old quickly).
I also did tour packages in Chile and Sicily that I loved.
I have also participated in several shorter programs within the US that were all satisfactory.
I know most of you think I ONLY home exchange, but that is not true. For some desitinations home exchange is not possible because the people on the other end cannot easily get visas to come to the US. You can't commit to a swap if you don't know if the other person will get a visa. So, home exchange really only works in the developed world.