I think there are some obvious flaws with the jury system, notably that it is incredibly easy for people to get out of attending jury service simply by stating that they are unable to leave work at a busy time. If this was common at my places of work, then presumably it is common elsewhere. Therefore you are not getting a reliable cross section of society.
My own experience as a juror a few years back left me uncomfortable at the thought that there may well be a high number of people in prison (or free) that shouldn't be.
We had a relatively complex case of kidnapping, extortion and assault with four defendants. After the initial address from the judge, and a few minutes of the prosecution's case outline we were sent to the jury room while a point of law was discussed. In that break, one of the more outspoken jurors had already established guilt and was detailing the case for the prosecution (before they had). This was a common pattern throughout the trial and it was down to no more than two of us to keep people aware of the fact that we needed to listen to both cases and sets of evidence before making judgements.
Worse still, there were at least four members of the jury that at deliberation professed their desire to leave early and had no opinion. I felt like a villain for demanding that we review each of the charges against each defendant as this was preventing people from going home. They'd either made up their minds long ago or had no opinion other than an early night was in order. If I had been shy or retiring, it would be likely that we would have finished within half an hour and all defendants would have been guilty on all counts.
As it was, with a bit of thought and consideration we reached what was probably a more balanced and fair verdict. That said, I felt at times that I was too easily able to argue a point given the desire to reach an agreement and leave was so strong.
Needless to say, it did leave me a little concerned at the processes in place that can lead to a conviction or acquittal. But is there an alternative? Perhaps stronger policing of attendance to get a proper cross section of society involved?