Okay I've now tested this a little further and it seems a little odd.
Performed an IIS reset, logged back in and the bar chart on our default dashboard shows values when you hover over them.
Switch to another dashboard with charts on and they no longer have values popping up when hovered over; back to the default dashboard again and the values aren't appearing there any longer either.
Logging out and back in will make these appear once again on the default dashboard until you swap to another as described above.
A little strange, any ideas?
That would be a bug then! (IMHO)
I was initially testing this via a console login running on our app server, having tested this again from a regular client machine these values seem to be appearing fine; not as bad as I first thought in the end but still not sure why this would behave in this way.
Maybe different patches installed?