Hi Pilou - what particular command are you using where you are concerned about the natural starting point of the curve?

In general commands in MoI are set up so that they are not sensitive to that, they usually will do things like automatically flip a curve to minimize twist (Loft, sweep, and surface blending do this), or they may detect which end to use by which end was closest where it was clicked on when selecting it.

So just in general I've tried to avoid needing people to take special care of which end of the curve is the natural starting point.

There is a plugin you can use here called MarkOpenCurveStart which will place a point at the natural start point of a curve so you could see which end it is:
http://moi3d.com/forum/display.php?webtag=MOI&msg=2888.11

I guess that there are a couple of specialized plugins that might be sensitive to it (and require manual flipping) like LineWeb, but I don't think that any of the regular tools should be. Some plug-ins may not have quite the same level of polish as the regular tools but they can probably be tuned up in the future.

- Michael