Just a note from the other side of the coin. I'm Jewish, and some superstitions stick with you. Jews don't buy things or decorate before the baby is born (or adopted, I guess, and on the way home). When my mom was pregnant with my older brother, she went and picked everything out, then they delivered it while she was in the hospital and my dad set it all up before she got home (with my grandmother's help, I'm sure). I asked my mom why she did it (she usually hates superstition) and she said that it made sense to her because if anything had gone wrong with the pregnancy or birth, she would have been devastated to come home to a nursery all set up, and then have to take it apart.
I guess with adoption we have a bit more of a "guarantee" that it will happen eventually, but I'm still wary about getting started ahead of time.
On the other hand, I'm still in the paper chase. Maybe when I'm waiting, and have nothing I can do to move things along, my opinion will change.
--Xanny