In the code there is a bit commented out which made bombs/missiles drop down when they were fired, apparently it looked at bit funny so Volition took it out.
As for having your ship 'speed' up when you fire off your secondaries, (or ballistic primaries now), in real life the only thing that would improve much is your acceleration and rotation, but Sandwich is right about the size comparison, the Boanerges for instance is just under 35 metres long and has a weight (well as used by the model in game anyway) of 686, I'd guess thats supposed to be in tonnes, your cyclops bomb is about 6 metres long, as for its weight dunno. Though having said that, the cyclops shouldn't be able to fit through the 'holes' the secondaries are supposed to come out of.
Anyway, what needs to be asked is, do you really want this feature, personally, I'd say yes, a bit of an increase in the acceleration and rotation speed ( and thinking about it the rotation damp as well ) would be quit cool, I't would be no problem to make it proportional to the amout of current total amount of cargo space divided by the total amout of cargo space. So how much does everybody think the amount should be? I'd probably say less than 25% maybe even only 10% ( in fact it might be cool to have it related to the mass of the ship divided by it total cargo space ).
If I remeber rightly , If you 'fired' off a missile/or bomb it won't actually push you back because of the action 'releasing' it, but rather because whatever the propellant is coming out of the back of it hits you and slows you down ( this would only apply to things that are in for purposes a very low G enviroment). But ballistic primaries would, in fact normal primaries would too, though both only by a tiny amout, unless it's some freaking huge bazokoid-blaster-from-hell type cannon. We've already got the shudder flag, would you really want to be pushed back by your firing weapons, I know I wouldn't. ( Though with that bazokoid-blaster-from-hell, mmmmmn. )
Robin.
EDIT: On weapons dropping: when fired, all the default FS2 ships fire them out the front, so the weapons are going to drop through the firing ship, I suppose you could create models which have bomb bays like the B52 et al, or have the missiles on Pylons under 'wings', then you'd have to have the missiles appear on the pylons until they were fired, hmmmmn be pretty sweet lookin' though.