its possible to observe players on multiple tables.
you need a "system" of who you observe for a certain period, say ten minutes. start with the players to your immediate left, b/c they affect your game the most, then go on with the next player to his left and so on. if you use a HUD, you only have to look for obvious lines, players potting bluffs but 2/3ing locks or something like that. at lower stakes you dont even need to make notes or reads on each players, since there are always some unimaginative ABC´s and rocks playing nothing but their cards.