How will a 3.6-4ghz o/ced Phenom II X2 555 compare to an i7 930 overclocked in desktop apps, video encoding, and games?
The thing you need to understand is that the 555 BE is as popular as it is due to its unlockability.
Unlock two extra cores and OC to 4 ghz, and it should do okay, though a 930 will walk all over it when encoding video in commonly-used encoding apps (there's one cherry-picked encoding app that the AMDZone guys like where Deneb can keep up, but . . .) In games, the 930 will have an edge, though it will not be so pronounced.
Desktop apps requiring nominal computing power will probably show little difference between the two.
If you do not unlock cores on the 555 BE, then it isn't going to be anywhere in the same ballpark as the 930, and certainly not worth the $90-$100 retail that one normally has to pay to get such a chip.
I don't know if Microcenter or Fry's has any deals on them yet, but in retail, the budget AMD chip to watch (in my opinion) is the Athlon II x4 445. It's a C3-stepping chip that is capable of unlocking to a 3.1 ghz Propus (quad core) OR 3.1 ghz Deneb (also quad core, plus L3 cache) depending on what you get. They retail for around $85.
At stock I would take one over the 555 BE since you lose L3 cache but gain an extra core for about $10-$15 less, making it about as good for games (depending on how heavily-threaded the game is) and considerably better for encoding. Still not in the same ballpark as the 930, but let's not kid ourselves: only Thuban can challenge the performance of Bloomfield, and even then, not in every app.