consider a user having 10 followers and another having 100 followers
it's much harder for the first one to keep up his xp with the one having 100 followers - e.g. the second user easily gets 10+ likes / 10+ comments on an interesting post while the first one hardly ever (as his cubbie posts are hardly viewed by others than those 10 people following him) !
to be completely fair xp should adapt on inactive lives (for say a week) and the should become "zombies" not counting into user's xp ...
besides there if it's considered there should be a weight mapping function - as the user should not be on a hunt for peers (remember this is not facebook).