As a partner channel manager it is handy to be able to login as the partner using the button on the contact object. The problem is that it does not seem to be possible to detect which contact is PRM enabled.
The only way you can find the partner enabled account is to manually open all of the contacts. If you have a big account with 15 contacts this is just to frustrating...Suggestion:
In the contact related list on the account object allow us to see what contacts are partner portal enabled or customer partner enabled.