LEDs put out more light per unit of energy they use when compared to CCFLs and especially regular tungsten bulbs, so there will be a significant reduction in energy consumption when they are used instead of CCFLs.
The issue with them is that when they emit white light, they become very hot and can burn out unless cooled. The closest color light they can emit is a bluish tint, though there may be workarounds with filters or the manufacturing process/LED design improved to become capable of white light. Assuming monitors are capable of extracting white light from the LED, the picture would be better because the light source produces more light within the same power envelope.
Some LCD's can be found with LED backlighting for about $600. I would project about 2 years before they are "mainstream" (in the sub $300 category and plentiful). We also may skip LED backlighting and just do Organic LED's instead.