https://gist.github.com/4534378 shows https://jenkins.ci.cloudbees.com/job/libraries/asynchPeople/ taking an inordinate amount of time in the callback. Clearly AsynchPeople.data() cannot assume that UserAvatarResolver.resolve is quick. UserGravatarResolver sometimes blocks on an HTTP connection to a web service, though this is cached. However every time it checks Mailer.UserProperty.getAddress, which in the presence of SubversionMailAddressResolverImpl examines every build of every project in every folder in all of Jenkins. This is so inefficient we probably never want to do it, much less synchronously in an HTTP request.
Besides People, the avatar is used in a couple of per-User pages, which is perhaps OK; but shown for every User in the HudsonPrivateSecurityRealm overview, which is definitely not OK.