Couple of thoughts I had while playing STO last night:
1) Could warp fields be used as a weapon? The equivalent of stalling their engines in your jet wash, if you will. Some sort of subspace interference between two warp fields that could cause a enemy warp field to collapse and force them back into sublight speeds. Makes for a handy hit and run tactic.
2) Cloaking devices are too perfect. There should be some localized affect that can be picked up on sensors as a result of mass and temperature changes. Stuff that a ship could hide. If I have a perfectly clear crystal ball floating in mid air, I might not be able to see it but it still causes a localized effect cause of it's mass, temperature, etc. There should be something disturbed that a ship's sensors can detect by the mere presence of the other ship.