As compared to a single C-C bond, the double C=C bond bears a planar geometry, shorter bond lenghts and higher bond energy.
The C(sp3)-C(sp2) bonds have a slight dipole moment because the olefin sp2 carbons are understood to be slightly more electronegative than the alifatic sp3 ones. This is explained due to the higher s character of the sp2 hybridization (one third) as compared to the sp3 (one quarter). The electrons in a sp2 orbital are slightly closer to the atomic nucleus and hence more attracted.
But polarity mainly depends on the E / Z stereochemistry of the olefin:
Alkenes cannot actually be catalogued as acids but, in relative terms, they are a million times more acidic than the corresponding alkanes.
This is proof of the higher electronegativity of the sp2 carbons relative to the sp3 ones.
Angles, lenghts and 
Angles, lenghts and 
