Phoronix has published an article about power consumption rates along the lasts versions of Ubuntu.
Here are the main graphs.
It's interesting because with the last kernel it seems that the power-consumption goes down a little bit, which is extremely valuable because as it is stated in Phoronix there are more processes running in Ubuntu 7.10 than in 5.04.
Thanks to Phoronix benchmarks we can conclude that with the last Linux kernel there is no revolution in terms of power consumption, but on the other hand we know that Linux Kernel people are working on this thread. It's also interesting how Intel has started to work in order to solve this situation. To do so they have started building a tool, PowerTop, that identifies which applications are consuming the most power and thus draining the battery. Eventually, this tool will allow developers to optimize their applications for maximum power savings.
If you want to read the full power-consumption article is available at Phoronix.