The statement from Syfy about the cancellation:
After painstaking consideration, we have had to make the difficult business decision to not order a season six of Eureka. But Eureka is not over yet. There is a new holiday episode this December and 12 stellar episodes set to debut next year, marking its fifth season and six memorable years on Syfy. The 2012 episodes are some of the best we’ve seen, and will bring this great series to a satisfying end. We are very grateful to Bruce Miller and Jaime Paglia, their team of incredible writers, and an amazing cast and crew who have consistently delivered a series we continue to be very proud of. We thank the fans for their support of this show and know they will enjoy its final season in 2012.At least with enough notice, the "satisfying end" mentioned in the statement is more likely, but this is still bummer news for fans of a show that have adapted quirky, compelling British science fiction stateside - especially after the series' best fourth season which saw a mind-bending parallel world storyline and some excellent guest appearances.
One final thought: Is Eureka enough of a fan favorite to create outcry and launch a "Save Eureka" campaign? If so, what will fans send in to Syfy to make their point (ala Tabasco for Roswell, peanuts for Jericho)?