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Dyntick will improve battery life, but there are also many services ("jobs") running in battery mode which shouldn not even be there. This includes e.g. indexing or probably dozens of non-optimized daemons which periodically do misc polling or log stuff, thus waking up CPU and hdd, up to eye candy like beryl/compiz which just warm up a GPU. Luckily with upstart it will be possible to dynamically turn various services on/off depending on whether laptop is connected to AC power source or not, maybe next Ubuntu could already approach Vista and XP on battery life.
I suppose X protocol isn't ideal for battery life either, as it has too many round trips and lots of "talk" to send visuals and other data through socket. Unlike XP where windowing system (widget based, so less talk) is in kernel and probably is able to keep CPU awake periods shorter (XP might be the battery king even compared to Vista).
Other mentioned problems sound easily solvable, or at least developers are aware of them and are being worked on (xorg 7.3, kernel modesetting + video memory management).