probably not celebrating the Seder. And, at least to my knowledge, there are no Buddhist Seders or New Age Seders or Ed Hardy Seders; Jews pretty much have a corner on the Seder market.
(Although, all things being equal, maybe I should write it on a chocolate bar.)
Update from john: [rubbing temples] To those of you currently chilling in the Epcot Bunker™, yes, anyone can make a lovely Seder. Apparently there are [insert comment count here] non-Jews doing so.
It's still Jewish.
That is all.