Might be a silly question, but I'm wondering, when do you consider a user a high rep user? Has the user to be in the top 10?/50? or does he need 10000+ rep, etc.
Just being curious...
There is not really a defined "greater than X reputation = high rep user." If a username is in the top one or two pages of SU users, then they are usually higher reputation users.
It is also relative to each site and the time it has been active. SO for example has 17k rep users on page 10 of the Users rankings. There are only 4 users currently that have > 17k rep on SU for comparison.
I like what DMA57361 was mentioning there in his second point. Any user that uses the new abilities given to them at certain rep levels and uses them to advance and improve the site would be ideal. Super User can always use more people to help edit and improve questions throughout the site. Of course, we need great answers also.
I'd like to add one more criterion to the conversation, so that a "high rep" user is anyone who:
Meets some expected rep score / percentile / ranking / etc.
Makes use of all their "powers", and does so correctly.
(ie, doesn't just use the basic "low-level" "powers", but actively acts as a high rep user).