On a child-meta site, viewing a user page provides a link to the user's page on the parent site. However, the reverse is not true.
The link from meta to the parent page is great, but having the reverse to complete the loop would be helpful too. Several times a day it seems I'll be viewing a profile on WebApps, but want to see their activity on meta. Switching tabs to do a user search works, but is somewhat annoying when a simple convenience link would do the trick. One example is that I find myself reading something on WebApps, recognizing it as a topic that's been discussed on meta, and wondering if the user has chimed in there. It also is a way to see if the user is truly involved by his/her participation and voting count on meta.