I raised an issue back in March about finding implementations of a trait in a similar way to a java interface.
Although I would still like that option, a comment on the issue also asked to be able to find usages of the base method when doing a find usages on an implementation. This is much more important and used to work.
If this is easy, it would be good to add it soon as it would make a big difference to me.
At the moment the work around is to click the "I up arrow" to go to the trait method and then do a find usages on that. Easy but a bit tedious.