The most important piece in a stereo system???

The preamp. If you have made a bad choice in the selection of the preamp, it is very hard to "correct" it with speakers, source or amp. If you have made a great choice in a preamp, you are 85% on the way to nirvana. Also, a lot must be said for synergy. I have seen great components (preamps, speakers, and amplifiers), while great individually, that just don't go together. No reasonable technical explanation can be given. Whereas the substitution of a "lesser" component will bring back the ease, effortlessness and beauty. Craig is right. The real question is not which piece is most important. It is which piece do you want to start with. I say that the best place is the preamp.

In a sense, everyone above to me seems to have a good point. But basically its the weakest link, isn't it and finding it will make all the difference. Apart from that, although I very much agree with what RCprince has pointed out, to my experience it have been the speakers. Only after finding the right dipoles, I've been really happy with my system.
Cheers to all and compliments of the season!

-Agree w/ Groovetuber and Audiocaptain, all links are important, some are easier than others to get a passing result with when you throw them into a system. The music (a whole 'nother can of worms), the recording and the ears and brain of the listener are at least as important. There are lots of audiophiles and high end dealers who have expensive gear and pathetcally mediocore cd or record collections. The average $10k system/Great material/ great recording/ receptive listener. ALWAYS beats a $100k system w/ most poular music/ a run of the mill recording in front of not very absorbent (most) listeners. I wish this wasn't true. A lot of great musicians who make excellent recordings make zero or next to zero $$ because of this.

The people and home around it.

I think all of the pieces are equally important, so I think that you should start with one piece that you really know and like the sound of: (speaker,amp, pre-amp,or cd player), then build the rest of your system around it to get the sound that you are looking for. One piece of equipment in your chain can drastically change the sound you are seeking, so audition carefully around the piece that you have selected to start with, and when your finished, you will have a sound that you should truly enjoy.