People are not understanding the Life Tap changes at all... It has absolutely nothing to do with the glyph.
Currently, Life Tap scales with spirit, which means the more spirit you have, the more mana it provides, but also the more life it takes away. With patch 3.3.3, it will consider SP instead of spirit when calculating how much mana you are going to get (and also how much life you are going to lose). Check out wowhead's Life Tap, it has the formula on it: http://www.wowhead.com/?spell=57946
This change will make Life Tap reward more mana, which is good, but it will also make it take more life away, which is bad (all of this assuming you have more SP than spirit, which you should have anyway, and also assuming the formula stays the same, just changing SPI for SP). If you are Affliction and have Improved Life Tap, that is probably a very good change for you. But even when that's not the case, I still think this is a good change. With the amounts of haste we are able to get nowadays, we cast more frequently and therefore lose mana faster. I'm finding myself OOM and having to Life Tap more frequently, even when the buff from the glyph is still up, although this depends a little on your spec and if you have mana efficiency talents. This change will probably prevent that. But we will have to be more careful, since Life Tap will take a larger chunk of our life away.
This will probably also overhaul all the Dark Pact builds, since it will probably not be on par with Life Tap anymore in terms of mana efficiency.