I assume that you are talking about NURBS, right? In that case, the direction does matter, because if the normals doen't match maya might end up twisting one or both of the surfaces to conect them, some times its not too obvious so you should pay some attention to the directions. You don't need to worry too much though, because if you get a twist just hit undo and reverse the surface direction once and attach again, that will probably do it.

to reverse the curve direction click "Edit NURBS>Reverse Surface Direction".

To check the normals of the surface just select the surface(s) and click "Display>NURBS Components>Normals (Shaded mode)". Obviously to see the normals you have to be in shadded mode (hit "6" when the mouse is over a 3D view). If the normals are pointing to the worng direction then just use the reverse direcion button with the default settings once.