A lot of the conversation going on depends on your style of healing and your healing assignment. If you exclusively raid healing, then WG, spreading LB's around and the occasional Regrowth to help your MT healer is pretty standard.

I'm also one of those druids that personally loves to have living seed. I never use HT unless it's a NS/HT macro, so the reduced cast time is junk unless your a Tree that use the old staple of Rejuv, LBx3, WG (for raid dmg) and then HT/Nourish to top off. If you have the 4 peice T7 bonus, Nourish instantly becomes a great heal (especially post patch withthe inclusion of WG to it's bonus effect) and for that reason I always pick it up. But make sure you have at least regrowth on the target before casting, and preferably a full compliment of hoTs (Rejuv, LBx3, Regrowth)

Natural perfection is a waste in PVE as you should never be getting hit, and I don't think the dmg reduction stacks with a Warriors Vigilence (which my warriors tend to run on the resto druids). It can be marginally useful in PVP, but even that's debatable.

Replenishment is kind of an unknown quantity atm. With several classes offering the mana return part of it I'd say it's unnecessary in 25 mans, just as much so in 10's but can be handy in heroics. If your tank is rage starved or your DPSers can use extra energy/runic power it can help in those areas...but again it depends on how often you have rejuv up on those classes.

Tranquil spirit I always take, because reduce mana costs never hurt and there aren't a lot of other (good) filler options to get you to the last teir.

Improved Tranquility is only really worthwhile if you spend most of your time in 5 mans, there Tranquility can easily mean the difference between a wipe or not. In Raids of 10+ though, you'll rarely if ever use it.

And don't overlook going deep enough into balance to pick up both Nature's Grace and Nature's Splendor. I have found both to make a huge difference in not only overall healing, but also in those circumstances where all hell is breaking lose and your just spamming everything you can get out to keep people alive....That extra .5 sec everytime you cast a regrowth (I find the proc rate to be quite suffecient) can be huge, and like a previous poster said, the extra ticks of your HoT's can make keeping a full stack on 2+ people much more manageable.

Hope some of this helps. But keep in mind that Tree druids are probably the healer class with the most options for different specs and styles, and in most cases all of them have their role in a raiding enviorment. Pay special attention to your glyphs, some combos and talents can be hugely beneficial.