I mentioned (when I first belatedly mentioned ion-drives, and how I'd previously thought about modding them in, long before the current version) how I had also been thnking of a simple companion 'orientator computer '(sounds like MechJeb is a far more complex thing, but never tried that and am just going from recent comments on here) that could keep the craft pointing forward (or outward, or any other relative direction I chose) throughout its orbit.
But all this was to replace my current practice of setting a regular engine on the lowest burn-amount I could possibly manage and every now and then adjusting the orientation while getting on with something more practical on an adjacent computer (or even on the other side of the room). And, like I said, I'm behind the times.
@Skyrunner: Simulation difficulties? Different rounding errors between how an engine thrust changes the orbit while running at 1s/s, 10s/s, 100s/s, etc would probably mean inconsistencies. Fuel use would be linear, but the changing n-th derivative values of velocity, acceleration and onwards might not be so easy to keep calculated so that thrusting under 1x warp gets you to the same position as the same thrusting under 100x warp, for example.
(I remember once having had a highly elliptical (nearly straight-up-and-down) Mun-hitting orbit from being near-stationary just under the limit of Mun's gravitational limit, and was hardly picking up speed. I increased Warp a few times. A few times too many, though and I actually found myself coming back up again, having apparently followed the (unpowered) track down to a sub-Munsurface lower orbital node and back up, but no collision occurred because the calculations regarding my orbital progress (with, by that time, much quicker progress along the track) had obviously sent me from a position of "safely" above it going down to safely above it going back up in a single blink of the engine, so no collision. If it had been timed much differently I would probably have been deemed to have crashed, of course, as one of the 'ticks' would have found me subsurface. I don't know if this (literal?) loophole is still around in newer versions, though, as I would have thought a simple trajectory-collision-point calculation would have prevented that from ever happening, even if it was part way through a nominal 'calculation tick' period.)
((Further ninjaed, in one way or another, by two others. Yup, much more succinct than me.))