Hi,
What can't be printed...I think the limit will be the human imagination and ingenuity, i've heard of food, drugs (medical) and metals all being researched in University Labs around the world. It's all very exciting and sometimes very SYFI.
What should be printed...is a whole different matter.
Licensing... There is a massive court battle about to happen in the States re copyrights. Similar to the CD, MP3, DVD, Bittorrent copying fights over the past few years. Toy makers, film makers (and others with copyright interests) are going to try and stop 3d printing. If it goes the way of MP3's then its going to get messy and differences in international laws (i.e. China allowing open copying - to a degree) will make it difficault to enforce. One to watch.
Personally I'm looking (when I get the mendelmax built) to print a starwars chess set for personal use and possibly for a few friends, will that mean I owe George Lucas some money ? who knows, I've paid to see the movies, paid to have the DVD's, and as a kid had the play figures, so I feel I've already heavily supported his copyright requirements, do I really need to pay more. The debate is hugh and maybe never resolved.
Just my 2p's worth (and theres another thought - what if 3d gets so good you can 3d print coins).... ohhh dear where will it all end....
Regards
Colin.