I've used them several times in Singapore, and 90% of the time they've been excellent - the other 10% of the time they were just heavily trafficked, but not "Dirty" - just puddles of water near the sinks, lots of paper towels in the garbage.
I do recall reading a front page story in the Straits Times about how the MRT had been hiring cleaning consultants to improve their already ridiculous (by my estimate) high levels of cleanliness.
I would love someone to do an analysis of all the horrible failures in San Francisco/Transit and compare them to Singapore, so we can understand why the heck one is doing so well, and the other one is so abysmal.