P.S. The below was inspired partly by my own experiences and partly by Diamond Geezer's various posts on TfL and the Underground in general.
P.P.S. Please don't sue me for this article, TfL. I don't have much money, and can't claim expenses unlike most British MPs'. If you're really aggrieved, I'll buy you a pint or something.
P.P.P.S. The image below was spotted on a wall near the Barbican Centre. No artists name was provided next to the work.

"Dear Passengers, this is an announcement from your Station Controller, on the weekend of [insert any here]. The following is a travel update.

The Bakerloo line will not be running in either direction due to the fact that the trains feel like rickety wooden sheds which will implode any minute, setting fire and incinerating all passengers within half a minute. In addition, there will be no Central line due to various engineering works which have outrun their allotted time. Meanwhile, ongoing upgrading work on the Victoria line will ensure that the line will be closed every other weekend until two-thousand-and-muthaf****n’ twelve, that’s 2012. Customers living in the Waltham Forest area should also note that, in the absence of the Victoria line running at Blackhorse Road station, they also won’t be able to get the Overground from Barking to Gospel Oak, which stops at that station, due to repair work on the track. But then who cares about the inhabitants of Blackhorse Road anyway? Frankly, it’s full of weirdoes. Who else would live on a street that’s had roadworks for at last seven years? Krypton Komics looks cool from the top deck of the bus, though. Maybe I’ll see a Deep Purple tribute band at the Standard one day. Residents of this area should note that there are replacement bus routes which go to nearby Tottenham Hale; said residents should also note that this bus route will be completely useless due to the fact that Tottenham Hale is on the Victoria line, which also won’t be running. For passengers in this predicament, we would advise taking another bus route to your destination, which will take approximately three days.
Moving on, passengers are advised not to use the Northern line in the middle of the summer, as (a) it will only confuse the hell out of you if you’re a tourist, what with it’s Byzantine complex of stops and different directions which will no doubt bypass wherever station you want to get to; and (b) the experience of being in a packed carriage in the heat will be roughly analogous to dying a prolonged, agonising death in a vat of one’s own faeces. Passengers are assured that when the new Crossrail line links up with Tottenham Court Road station in 2017, we will ensure that there will be still be an irritating trustifarian busker in the pedestrian tunnels regaling you with mediocre covers of Bob Marley ‘classics’.
Customers should also note that the Waterloo & City will be closed on Sunday, just because it’s always been closed on Sunday, as no-one in control can be arsed to run it. Jubilee Line will be closed in its entirety, which we can assure has been done entirely to spite those poshos who (a) can afford to live in West Hampstead, and/or (b) work in Canary Wharf. The District line will also be closed, because, well, who do you know ever gets the District line anyway?
Meanwhile, the Docklands Light Railway, a genuinely enjoyable jewel in our 'crown', is closed completely due to the fact that the O2 venue has turned out to be a giant spacecraft that’s lifted off and burnt the tracks.
All other lines will meanwhile be closed due to various engineering work that’s clearly taking twice as long as we initially forecasted, mainly due to workers striking / eating peanut butter sandwiches for too long / going down the pub / spontaneously combusting. There will also be no National Rail, due to leaves on the track, everywhere, all at once. Customers should note that the exception is Southern rail, who will conveniently fleece you even if you do have an Oyster card.
Please have a pleasant journey. Eat more vegetables. Watch X-Factor. Shut up and be happy, and carry on buying Oyster cards at ludicrous prices, even though your card will be rendered obsolete half the time due to the fact that the line that you actually need to use won’t be running.

On behalf of TfL staff, thank you for listening. We are transforming your tube. Message ends."