JKR has updated her site today -- WEBSITE SPOILER!

[Hagrid]

No: HPFGUIDX 158302

> "potioncat" wrote: (snipped)
>
> Back to the IC. One of the older theories here has been that James 
> gave DD the IC for the Order's use. ..
> 
> I don't know. That isn't very bangy unless whoever had the IC is 
> important. Hagrid? Snape? Lupin?
> 
> Potioncat, who thinks the address was 12 Gryffin Place.

Aussie:
Two People needed to be protected because of the prophesy. One was 
Harry. The other was Neville.

The Potters had GH and SK to hide behind. The Longbottoms? They may 
have wanted the IC to hide/protect Neville. 

After the attck on the Potters, the Longbottoms were Crucio-ed by DE 
trying to get information. When the DE turned up at the Longbottom's 
house, where was Neville? Maybe baby Neville was in the room, but 
like Harry on the Tower, was under a spell to not move or make 
noise. Neville wasn't seen because the IC was over him. 

(Neville's mother may also have made sure the IC wouldn't move off 
the baby. She stuck the corners down using ... YES, you guessed 
it ... that famous chewing gum!)

aussie (Which of my theories do you like? 1. DD may have thought 
James was the spy and confiscated the IC to stop James sneaking 
around. GH may have been James house arrest. -or 2. Neville was the 
VIP that needed the IC.)