OK... I want to add to the post, not just act silly (but really, who's acting =P)
I changed to disc around L65 or so. I was also just really learning how to heal groups at this time and never used either PI or PS. They were conveniences that weren't really necessary. When it came time to incorporate them into my game, I was unsure how and where to use them. So skip them if you like, but if you do add them, start using them right away or they are wasted points.
FW is a semi-PvP talent. The crit portion is mainly a continuation of Holy Specialization with the added value of affecting non-holy spells (uh, just Mind Blast I think?) as well. As far as I am concerned (at max level), crit is good- more crit is more gooder... with some exceptions.
FP... 4% more? Again, healing is good- more healing is... well you get the picture. Faster MDs may or may not be beneficial to your playstyle. It has its uses in PvE, but really comes into play more in PvP.
FW is a proc. FP is a constant. Until you get DA, I wouldn't really worry about crit. My crit fluctuated wildly while levelling. Don't sacrifice a clear upgrade to maintain a particular crit %, you'll get that crit back later.
PI is just plain cool. Use it on yourself for fast, efficient casting. Use it on another caster to give them a boost. I had a thread about this a while back...
here it is. After using it in various circumstances, you will really get a feel for just how good a spell it is with a relatively short cd.
Incidentally, I was told that the haste from PI does not stack with Bloodlust/Heroism. If I am planning on throwing it on a caster, I wait until heroism ends before casting it.
Other places for PI:
-macro into PoH (along with Inner Focus for fast, free group heal) or Gheal.
-macro into Mana Burn for PvP.
-macro into "use" trinkets.
-macro into rez for cheaper, faster resets.
(Does it show that I like mah macahros?)