I have encountered the Shere machines with signs saying they are not accepting cash, and/or that they are not giving change and to use exact money if paying by cash.
However, in all cases they actually all still accepted cash and gave change (funnily enough they did not accept in the new pound coin, but gave it out in change - furthermore, if paying halfway for a ticket and pressing cancel for a refund, the machine actually acted as an exchanger of old pounds to new)
Also they are quite unreliable when wanting to top up an Oyster. They will often fail to read your Oyster, but the way to fix it is to begin the process of buying a regular ticket including actually putting some money in (which is how I discovered the unexpected behaviour in the previous paragraph) and cancelling. This somehow resets the machine and it will then read your Oyster just fine.
I have also encountered the extremely slow behaviour mentioned in the previous post.