Wazz up PMan?
Chi sao & hubud are both touted as being sensitivity exercises. They develop the ability to sense where your opponent limbs are, where thet are going and therefore where the opponent is open to attack. Personally, I believe that hubud tends to develop more timing than sensitivity. This drill helps you develop the ability to read attacks, defend and counter his strikes (with strikes, joint locks, and disruption of his balance).
These drills can be great fun, but IMO they can only take you so far. Since they are somewhat scripted... they are probably somewhat unrealistic. IMO, standing clinch work will probably develop these attributes faster and develop the the ability to actually apply these skills in combat.
Of course.... I might not know what I'm talking aboout! Hmmmmmmmmmmmmm...................................
~Kev