What was annoying was that I found myself unable to buy the day tickets for the Metro as the station machines didn't sell them - but that's probably because I didn't know where to ask. Even big stations didn't seem to have conventional ticket offices so I was a little confused (take note Boris), but it didn't really matter as most fares are about 3 or 4 kwai (30 or 40 pence).
They don't sell them at the machines. They (24-hour/72-hour "rangers") are only sold at ticket windows (read "booths" rather than "offices") which all stations should have at least one in each concourse and must be staffed from first service to the last. They are not easy to find though. Machines only sell single tickets iirc.
As for security, if you are carrying a rucksack or large shopping bag, it passes through a scanner on entry to the network where a staff member may or may not look at their screen and it is returned immediately.
They are mainly in their late 40s onwards and were laid off en mass from state-owned factories from the mid-1990s onwards. No-one would employ them due to whole industries collapsing and oversupply of labour in the unskilled sector. It threatened social stability because suddenly they could not feed their family. As a compromise the city government created lots of fringe jobs for them on the understanding that they would get a living wage, but they would not be expected to do much either.
I would be surprised if a terrorist is ever caught by that process. They provide a presence, and can be helpful if you are in need, but aside from that I doubt they achieve very much.
I was surprised at how long the dwell times were at the Metro stations, which are gated on the platform to enter the train like the Jubilee Line. Comparable systems like our own dear Tube seem much more efficient.
Lines 1/2/3 are still not gated in certain areas, but platform gates have been a compulsory requirement since the construction of Line 5 (built before Line 4) due to the number of suicides in the earlier years of operation.
Dwell times are longer partly because schedules are drawn up to cater for large-ish crowds at many stations throughout the day, and partly because of the limitations on the signal infrastructure (not entirely sure about the details as it's not really my area of expertise).
Did you notice that the driver has to leave his cab at every station? That also contributes to it. I don't know why they do that, presumably to make sure that it was all clear before departure I would imagine. (Hello, mirrors!)
Oh - and owing to a misunderstanding of names, I didn't pay enough on my first journey in the city. The barrier wouldn't let me out, so I went over to the lady who sign-languaged I was one kwai short - she gave me a ticket for that when I paid her, and it did let me out. I don't know if this is general policy or she was being nice to a tourist, but no £80 penalty fare!
There are Penalty Fares, 50 kuai iirc, but only for when you jump the gates and travel without a ticket. All you have to do if you override is to make up the difference in fare and you will be on your way.
If you exceed the maximum journey time, which at last check was 3 hours but may have increased since the expansion a few months ago, you will simply get an exit error and be referred to the customer service window, where in addition to the single fare for the journey made, an additional fare equivalent to the lowest single fare in the system, currently 3 kuai, will be deducted/charged. There is none of this palava of deducting two maximum cash fares.
If you are thinking of going to China, Shanghai really is a must-see if you can only go to one place. Just about better than Beijing (but the pandas there are more numerous in the zoo).
I know. I spent half of my childhood there (so I should probably declare my conflict of interest here). It really is an amazing place. Both Shanghai and Beijing are places which I think should be visited at least once in anyone's life. Shame about the smog and pollution, which is much worse in Beijing, so yeah, if I am forced to choose just one, I know which one I would go for.