I have two years ago, it was actually a trip to Switzerland but we had a visit in Liechtenstein too :) We saw Vaduz along with the prince's castle. I guess we saw him or one of the royal family, cause there was a beautiful black Ferrari which had passed us by ;) It's a little but really nice place, I can recommend it!
Lichtenstein is a very pleasant little state. Vaduz is quite beautiful and one of my best memories is a hotel from which we could see all the Valley and the mountains, a place made entirely out of wood which is uncommon in Western Europe. I personnally prefer the principality of San Marino in Northern Italy because it is a Republic, but Lichtenstein is fine. I think there are some days when you can visit the prince's palace, but I'm not a particular admirer of princes - they're financial leeches on society and should frankly be scrapped.