Hi,
There's a function called Move Components in the Edit Polygon -> Texture scroll bar, it's useless if you need to scale UVs with exact values. About keeping a bunch of UVs proportional, it's just a question of having a good eye, as nothing allows to have numerical indications for exact UV proportions in Maya. Maybe if you do only use one same type of projections when mapping (which seems very hard to me), you can set it with the same exact scaling values ... But when using planar and cyl projections (for example), there's no way to keep exact proportions between them ... Thou, if anyone has a solution or a tip about it, I take !
Alban