Is there any reason except weight and price for which one would choose the 40-150?
The 40-150mm is optically better and lets you open to F/4 at 40mm, while the 14-150mm is already F/5.6 by that focal-length, so you get more light in until you get close to the end of the zoom range.
For sharpness, it depends which side of the 40-150mm range you prefer. At 40mm, the 14-150mm is noticeably sharper than the 40-150mm. At 150mm, the 40-150mm is noticeably sharper. See sharpness samples at all F-stops here and here
Vignetting is terrible on the 14-150mm at both ends of the zoom, while moderate on the 40-150mm and only near the widest aperture. The 40-150mm lens also shows less distortion.
I think that Itai has covered it pretty well. However it's worth remembering that another contender is likely to be only a couple of months away; the 40-150 f/2.8 pro lens from Olympus which, last I heard, is due out in September. (Referred to in the brochure that can be found here.) Depending on:
(a) How much you need a lens now (I'd assume that you already have one that covers up to 40mm, because the 40-150 alone would be a bit limiting as a sole lens);
(b) What your shooting needs are; and
(c) What your budget is,
it may be worth waiting to see whether that's a third option. Based on the specs released so far it's likely to be much better in optical and build quality (if considerably more expensive) than the two above.
For myself, while the 14-150 would be convenient I'd prefer the quality of the dual 12-40 f/2.8 (which I have) and the 40-150 f/2.8 (which I'm hanging out for).