Water Bottle Cage recommendations?

while training for my HIM last year, I had two on the frame plus the Profile bottle cages on the back.  I never wanted to count on there being a fluid stop at a specific location on the course.   

For the race itself, I got rid of the rear cages and added an aero bottle.

How much fluid do you really expect you'll need? 

Unless you are the slowest swimmer in the last wave -AND- the slowest cyclist, you should be able to replentish at aid stations.  If you are that last-person-in-front-of-the-street-sweeper, what are you going to do for the run?  (Most races hold the aid stations open through the cutoff, but they may run out of stuff towards the end.)  Now, you might want a 4-bottle setup for training rides, especially in hot weather.  I rubber-banded a bottle of water onto my aerobars and I've carried an extra bottle in my jersey. 

You shouldn't have to skip more than one station.  If the first one is out, they should have radio'ed to get additional supplies to the second one (or make sure they do).  If you're completely out, grab two bottles in an aid station with supplies. 

You could also wear a camelback (if you're really that slow, the aerodynamic drag won't be much of an issue). 

I think the primary consideration for additional cages is either (1) so you can do long self supported training rides or (2) if you use a formula not on the course, i.e., Infinit.  Both of these are true for me.  I like to be able to load up with 3 bottle of infinit and one water and know I can make it through 80 miles on that alone without having to stop or find a liquor store etc.

As for the holder, I like the Minoura double bottle holder.  The bottles sit more upright so when going over rough road you can basically keep the bottles from ejecting by moving your butt back a touch.  it's cheap (like $15) and works well.  Got mine from trizone.com

The hydro tail is supposed to work well and not be a bottle ejector, but it's more expensive.