I tried to customize the new combat log, and it actually wasn't too bad.
/script TEXT_MODE_A_STRING_TIMESTAMP = "[$time]"
/script TEXT_MODE_A_STRING_VALUE = "$amountType$amount"
/script TEXT_MODE_A_STRING_VALUE_SCHOOL = "$school "
/script TEXT_MODE_A_STRING_VALUE_TYPE = "($powerType) "
/script TEXT_MODE_A_STRING_1 = "$source $spell $action $dest $result $value. $timestamp"
/script TEXT_MODE_A_STRING_2 = "$source $action $spell $dest $result $value. $timestamp"
Basically all this does is make the end of the line (Critical) Nature 200. [12:01:37]
Instead of the default order of 200 Nature (Critical), and timestamps at the front. Note that timestamps do not display if you don't enable them in the Blizzard UI.
You can find the rest of the strings in FrameXML/GlobalStrings.lua.
http://wdnaddons.com/