One thing that threw me for the longest time was that you have to get an even number in a given skill to get a full attribute point. For example if you're doing a warrior and raise Block and Heavy Armor 3 skill levels and Armorer 4 skill levels you've done 10 points in endurance skills but you won't get 5 points just 4 (2 for Armorer and only one each for Block and Heavy Armor). If you raise Block 2 skill levels and Heavy Armor and Armorer 4 you get the full 5 points. Something to remember if you decide to spend money to train a skill those 5 levels. You have to get one more skill level on your own to get maximum attribute bonus for that experience level.
As far as whether it's worth it to get the triple 5's I'd say it can make a big difference for a melee character. I used to do the Thief Birthsign to get that extra 10 points in Luck and I'd boost Strangth, Willpower and Agility (the latter two because the gains were so easy at the lower levels). For a change I switched to the Warrior and stayed focused on getting Strength and Endurance maxed out and it's made a huge difference. Right now my warrior character build is:
Race: Nord
Birthsign: Warrior
Custom Class
(Strength / Endurance)
Specialize: Combat
Skills:
Armorer
Block
Blunt (or Blade whichever one you prefer)
Conjuration
Destruction
Illusion
Marksman
Of these Major Skills I only use Armorer and Block (it's easier to control how fast you level these than Heavy Armor). For actually fighting I use Blade and Hand to Hand (to boost Strength) and Light Armor for protection. The Light Armor works well with the steady raises to Athletics just from running around to make Speed my third five for the bonus it gives to Fatique and for the fact I can actually play tag with deer now

.
With this build you start with Strength / Endurance at 65 each. By Level 8 you can have both at 100 and you can go back to your Heavy Armor (you'll have access to Dwarven by this point instead of Iron/Steel which are basically dead weight) and Blunt, which are still sitting at a decent 40 skill level, and start maxing out Agility, Willpower and Speed for the Fatique bonuses.
Downside to this build is that levels 5,6 and 7 go by pretty slow as you're getting up Blade (stick with daggers) and Hand to Hand. You also have to make do without Bound Weapons, Chameleon and Light spells for those levels and a ranged attack for those pesky archers placed up on a ledge.
Plus side is once you're at Level 8 you can forget about the fives and just do what you want since your key stats are covered. So a little short term pain for long term gain.
For casters you could probably work something similar but focussing on Destruction and Restoration (since those are the toughest to raise) to boost your Willpower.