Some of these things are issues that are being dealt with, some are bugs, and some are things that will probably never be implemented in the default behavior so you'll just have to code your own method.
Ashley has mentioned the possibility of changing the push-up routine of the platform object so that it pushes out of solids in the direction it went in instead of always defaulting to up.
As for the window dragging, it's a bug. I believe I reported it a while back, but that might have been for the sound object messing up when dragging the window.
I've never had much success with vertical moving platforms. I've always had the jittering effect you described. But... the last time I tried making a vertical platform was before the introduction of adjustable gravity settings at runtime and the ability to set the velocity of the platforming character manually.
The method I've been thinking of (but haven't actually gotten around to trying yet) goes like this:
1. Measure the distance from your platform sprite's hotspot to the bottom edge of the sprite in pixels.
2. For your vertical platforms, make an image point exactly that number of pixels above the top edge of the platform.
3. Make a foot detector for your platforming sprite.
4. When the foot detector is overlapping the vertical platform (and the character isn't jumping) do the following:
- Turn gravity off for the platform object.
- Turn Ignoring Input on for the platform object.
- Set the platform object's xy to (self.x, (platform.ImagePointY(1))
- Manually intercept the controls for Left, Right, and Jump
- If Left or Right is pressed, manually set the horizontal speed accordingly
5. If Jump is pressed, or if the detector is no longer in contact with the platform, turn gravity back on and Ignoring Input to off.
It might need a little tweaking, but I think it could work. Possibly. Theoretically with no gravity to fight against the jitter will be eliminated.
As for intersecting the sides of horizontal moving platforms, you'll have to code your own push-out routine to avoid being popped to the top automatically by the platform behavior. At least, until the new push-out method is done.
Finally, as for your question about whether or not Construct can be used in a production type scenario for a platform game. I'm assuming you mean "can you currently make and release a bug-free game of commercial quality." Well, probably not. Construct is still in beta. Either you can wait for v1.0 or you can help out with bug testing and wait for v1.0.
It is however quite capable of making playable games, if not perfect ones. You just need to be aware that things will probably be a little buggy for a while.