I have found recently that trying to tag users in a post doesn't work for all users. One particular user Joe_Cunio . I am unable to tag in a post as I cannot find him even on posts that he made and I'm commenting on.
Additionally another user with the name egg_i , If I search for "egg_" I can find him but if I type "egg_i" I cannot find him.
And for CA employees who originally had their pmfkey as their username and now have a different name, they still show in @ as their pmfkey. This makes it difficult to ensure you are tagging the right user.
Overall I think the @ wdiget needs some improvement. If I can't immediately find what I'm looking for I should have an overlay similiar to the link widget where I can do a more advanced search, filter the results to only users and see more results.. There are way more than 10 users in the system with @ Joe in their username but today I can only see up to 10 users, so I can't find who I am looking for.