Tipster Fortine linked us this thread, where a handful of Warlocks are reporting a return of 15% of their max mana at a cost of 5% of their max health, without the Improved Life Tap skill. The question, of course, is whether this is intended or not, but with no blue confirmation, it is hard to say at the moment if this was someone misplacing a piece of code, or an actual intended change.
It's definitely an improvement from the last iteration of the skill. However, scaling concerns could come into play. 5% of max HP may make this a buff in PvP, with Warlocks able to give up less health per Life Tap. However, PvE Warlocks will still have to lifetap more often to get the same amount of mana as before, which will mean less DPS for them while they wait on global cooldowns, and more Stamina will still technically be liability for them, even if not as much as before. We'll see if it's tweaked further though, it seems likely that the 5% figure on the HP may be deemed a bit too low, and we doubt Blizzard meant to buff Life Tap in PvP while nerfing it in PvE.