Against the common target, fighter's, the 88 isn't that effective (though I HAVE shot down a few of them with it 

).  Against bombers, it's a different story, especially if 
all the 88's are manned.
What gets me though is, from what I've heard about them is that a blast within 8-10 meters would almost always bring a bomber down, even the B-17.  Within 8 meters and you were going down no matter what you were flying (minus Lady Luck's Grace).  I am hoping someone has access to books on this bit because it was a LONG time ago that I heard this.
Below is an example:
http://www.youtube.com/watch?v=ysQqi0-6His&feature=relatedOurs isn't that deadly, as I've landed shots like this against bombers only to see em fly off with an oil/fuel leak.
The few things that have to be taken into account about the 88 crews are as follows:
1) They had AMPLE time to get setup for the incoming bombers, either via radar, observers and/or interceptors.  Those bombers had to fly for 6+ hours, we only have to fly 15-30 minutes depending on alt to get to target (though we do have that lovely neon icon to help us for alt 

).
2) They had a LOT of flak guns protecting a target (depending on target of course).  We have 2-4 depending on base.  Even the Capital is woefully under-protected compared targets of equal importance in WW2.  (Though I WILL say that it takes out my formation of B-29's like a 262 flying over a CV. 
 
)
As for the hit percentages, it would depend if you meant a single gun crew or a flak battery.  I would guess better than us, regardless.  A majority of the bombers lost were to flak, not fighters.
This bit is a little unrelated to this topic but, if somebody could tell me what show this was from, would be much appreciated. 
http://www.youtube.com/watch?v=zp1teqL-TLc&feature=relatedI remember watching it a long time ago, but I bloody well can't remember the name of it. 
