I remember my jury service in 2012 (as above), I was selected twice, got challenged twice and only ended up being at court for a couple of days - never sat on any jury.
One case (from memory) that came up - not one I was selected for - was a murder trial, and it was going to take 9 weeks. They selected the jury and seated them, right after which someone in the jury said they couldn't commit to doing a 9 week-long trial after all. So they had to go through the entire selection process all over again.