StreamOfTheSky
Adventurer
To me, huge creatures need to seem HUGE. If they can only move 5' despite having stride lengths of 15' they seem more like Jabba than a Frost Giant.
If they're that big and still have a human's speed, then clearly they're a bunch of clumsy oafs unable to manage a longer reshuffling of their position safely.
As for IH, the rule I've considered is 5 ft per 30 ft of speed, speed 30 would 5 ft step, speed 90 would 15 ft step, and so on. I'd probably have to limit it to ground speed and swim speed, though. Fly would otherwise give an automatic 10 ft step, and a Druid with Improved Flight feat (to make it perfect maneuverability, if it mattered) could get a 15 ft step with a 2nd level spell, Master Air (Fly 90 ft good, round/level).
/threadjack
Also, I completely agree with Jeff.