BotG stacks additively. Meaning with two points you only get right over 2% instead of 4. There is really no reason to take 2/2 botg and only really should take 1/2 if you are dropping massive amounts of regen points and have a ton to spare.
Per Dendrek: Rejuvenation is affected by several additive effects, meaning that although BotG should increase healing by 2% per point, it actually increases healing by MUCH LESS than 2%. In fact, it's worth something close to 1% increase per point. That's a 1% increase to Rejuv's healing, not a 1% increase to overall healing. It's very likely close to a .5% increase per point to overall healing. That amount is so small it almost makes those wasted talent points.