I think BusTimes is really useful. Of course it has its limitations. Sometimes buses just don't track, more often they track as the wrong vehicle (doesn't worry me too much). If the timetable data is wrong then you can get very some odd results. But it is the best source of timetable information, most usable for finding information and planning trips etc, although I would always check the bus company's own website before finalising any plans. The ability to search on a particular place to get all services from there, plus the details of exactly where different routes stop, with a link to maps and StreetView is really helpful. The maps by company and the maps generally are useful. On top of that the tracking of buses is really useful provided you accept the limitations and that some information is not always correct or complete. While actually out on the road the live tracking comes into its own as it helps make decisions on whether to get a particular bus or wait for the next one, whether they are running at all / on time / late and what type of bus it is. You just have to accept that possibly a bus tracks but it running out of service but there are often clues. Also you can look at particular journeys from previous days and see whether they ran on time and what their previous journeys were to get an idea (not guaranteed) of what may happen.
Here's a wonderful example of where it didn't work for me in the Manchester area in December - posted on the Trips thread, I was coming from Mossley on the First 350:
Now here I was deceived by relying on BusTimes. I know this can happen and accept the risks of using it and here it was a case of ‘garbage in garbage out’. I intended to leave the 350 at Delph and continue on to Oldham using the Nexus Move 356 via Denshaw. But checking on BusTimes the map of the 356 and the vehicle check showed only two buses out (should be three) and my intended one missing. I did not check the map of all Nexus Move vehicles. So I decided that I didn’t fancy waiting half an hour at Delph for a bus that might well not turn up – Delph is an attractive village but it was cold, I was still cold, I had been there before and not much appeared to be open as I stayed on the 350 round the loop at Carrcote. So I decided to stay on the 350 and continue to Oldham that way. Much later in the day I looked again at the 356 on Nexus Move to see what had happened. It showed bus 140 starting out on the 356 at Delph at 10.14 on the journey I intended to take. So I looked to see what the bus had done earlier in the day. It showed it out on the 184 going to Marsden, Oldham and Marsden. Odd I thought, the 184 only runs in the evening, the daytime service is with First. So I looked at the maps of these journeys – they were the missing 356 journeys, nowhere near Marsden! This bus had been out on the 184 the previous evening so I assume the morning’s driver hadn’t changed the route on the ticket machine back from 184 to 356 so had fed rubbish information to BusTimes while actually carrying out all the correct journeys. I think that if I had looked at the map of all Nexus Move vehicles at the time I would have picked this up – but I didn’t.
But for the whole of the rest of the day BusTimes was very useful. For example I took an earlier 163 from Middleton to Bury than planned because I could see the next one was late. I actually left this at Heywood as I could see a 471 was coming soon after. At Salford I knew when 100s were coming towards Eccles, at Patricroft I could see what was coming to move on to the Trafford Centre.