The Munich easy everything, and perhaps others, have changed the pricing arrangement.

First of all, all purchases must be made from vending machines and the machines don't give change.

Second, you can still buy time by the hour (not sure if it is still demand based) but most of the ticket sales seem to be "period" based.

For EUR 0.50 you can buy a "one logon" pass, which is really just a ~45 minute pass. Additionally you can buy daily, weekly and monthly passes. Now here's the catch -- they've takin a cue from airline pricing -- the earlier you buy the ticket, the cheaper it is. For instance, a monthly pass for June might cost EUR 5.00 in march, EUR 10.00 in April, $15.00 in may, and $20.00 in June (I don't remember exact prices, but you get the idea)