After re-reading this thread, I wanted to make a few more comments.
Currently, the rules for vehicles feel a little incomplete, to me. Yes, the stats exist, and the weapons are all kinds of cool. Yes, it's cool to move and shoot. However, I feel that some key aspects were left out.
Firing arcs. This is a limiting factor. Vehicles are not, generally, supposed to have the 180º firing arc that non-vehicles, generally, have. Further this forces vehicles to have to manuever to get their shot. This brings me to antoher point.
Turning. I do not feel that this was done well. Currently, turning is not much of hindrance for vehicles. This is so true that on occasion, my opponents and I sometimes forget that vehicles even have to turn, and move them like troops! Many times I've caught my opponent sidestepping with his EDD, only to shrug it off as, "eh, so what." The truth of the matter is that vehicles are only entitled to one turn per AC. Combined with a 90º fire arc, this can severley limit a vehicles ability to get its weapon on target.
One last point. Reverse movement for vehicles. For some, it is almost moot, as their turn radius is such that it barely hinders them, so they wind up turning, moving normally, and turning again with no real face change.
If I were going to re-write vehicle movement, it would resemble the following:
Vehicle Turning
Vehicles are limited to one turn per AC. The turn, itself, may be performed at any point during the MV AC. The vehicle's chassis determines its turn radius, and terrain limitations as follows:
Bike (90°) - 1/2 MV through Rough Terrain, 1/2 MV through water no deeper than 1/4", cannot MV through Limiting Terrain, may Pivot by expending entire AC turning and not moving any distance.
Wheeled Small (90°) - 1/2 MV through Rough Terrain, 1/2 MV through water no deeper than 1/4", cannot MV through Limiting Terrain, may not Pivot.
Wheeled Large (45°) - 1/2 MV through Rough Terrain, 1/2 MV through water no deeper than 1/2", -1 MV through Limiting Terrain, may not Pivot.
Half-tracked (45°) - 3/4 MV (round to nearest 1/2") through Rough Terrain, 1/2 MV through water no deeper than 1/2", -1 MV through Limiting Terrain, may not Pivot.
Tracked (45º) - 3/4 MV (round to nearest 1/2") through Rough Terrain, 1/2 MV through water no deeper than 1, may Pivot by expending one AC turning and not moving any distance.
Skimmer (90º) - No terrain penalty, +1 MV if AC spent only on calm water or other perfectly smooth surface (snow, ice, asphalt, concrete, etc.), cannot MV through Limiting Terrain, may Pivot by expending one AC turning and not moving any distance.
Flyer (45°) - No MV penalties, cannot MV through Limiting Terrain that is at its current altitude, may Pivot by expending one AC turning and not moving any distance.
Walker (90°) - 1/2 MV through water, may step over anything less than 1/2 its SZ in inches (height and/or width), may Pivot by expending one AC turning and not moving any distance.
A vehicle that may Pivot may do so up to 180°. All vehicles may move up to 1/2 their MV in reverse, in addition to any other penalties. No vehcle may move through another vehicle, even if it is from the same squad. Vehicles must have a 1.5" gap in order to move between two friendly models or a friendly model and an obstacle, or to move between enemy models. At this time, there are no rules for ramming and/or overrunning.