What have you done with UDAs?

[Brian Schott via Digitalmars-d]

On Monday, 22 June 2015 at 19:09:40 UTC, weaselcat wrote:
> I never seem to use them for anything, has anyone else done 
> anything interesting with them?

Semi-hijacking this thread:

I recently made a few pull requests to get better support for 
UDAs into Phobos.

https://github.com/D-Programming-Language/phobos/pull/3356
https://github.com/D-Programming-Language/phobos/pull/3421
https://github.com/D-Programming-Language/phobos/pull/3363

The last of the three is stuck because nobody's looking at it. 
Can those of you who use UDAs take a look at these and confirm 
that I haven't made any dumb mistakes before the 2.068 release 
goes out with them included?