In v0.13: dumpwallet "dumps all wallet keys in a human-readable format." (according to console help).

First, it's hard to tell where it dumps them.

Arguments:
1. "filename"    (string, required) The filename

I executed the action and couldn't find the file. Another way to look at this is "I executed the action and nothing happened".
Well, it turns out it did work, but the file ended up in the Bitcoin "root" directory (for me, c:\Bitcoin).
I bet some users would think that the command simply didn't work and you can see where it goes from there.

Second, the action behavior isn't particularly intuitive.
For example, I'm in E:\backup and I run
c:\bitcoin\bin\bitcoin-cli.exe dumpwallet wallet.txt
I think this shouldn't dump the wallet to c:\bitcoin\wallet.txt.

dumpwallet e:\backup\wallet.txtworks as expected (both from debug console and from the CLI).

This could be classified as a doco bug (e.g. change "The filename" to "The full path and filename"), or it could be improved in the code.

OS: English Windows 10 x64.