Where does the default username in options come from? <login>@<hostname> is quite confusing from several reasons:
1) If you want to change it, for example just add one letter to login and press OK, you are presented with warning
dialog that it is not valid email address. But then the original is not either.
2) If you change it in options to valid email address and press OK, then you delete the created hgrc (because you want
to yous your Mercurial.ini at mercurial install dir), just opening the options and pressing OK will create the hgrc
again. Maybe a button "set" or something like that might be there. You can say that you should press Cancel if you don't
want to use what is in options, but most people will pres OK, because they know they did not change anything so they
don't expect to be any difference from before.
3) Invoking Mercurial | Properties... does show other username than is used for push. I think that if you did not change
anything there (thus <project>/.hg/hgrc is not created), there should be present a username that will be used for push.

I think that the default username should be determined looking into hgrc or .ini. The question is what should be there
when no username is found in any of these files, perhaps the <username>@<hostname> but then the behavior of options has
to be changed as stated above.

I am not sure what would be the best way to solve this, but in current state is really confusing.

NetBeans IDE Dev (Build 200803170003)