JKR has updated her site today -- WEBSITE SPOILER!

[Eddie]

No: HPFGUIDX 158473

> Nate wrote:
> didn't Dumbledore take the cloak from Harry
> at Slughorn's then give slip it into Harry's pocket when
> they got to Hogwarts?
> 
> ibchawz responds:
> DD actually told Harry to keep the IC 
> with him at all times, even at school.  If I am not mistaken, this 
> conversation occurred in the Weasley broom shed after they left 
> Slughorn's.  When Harry went to Diagon Alley (prior to start of term), 
> he had his IC with him.

Eddie:
Harry had the IC with him even later on the train.  He used it to spy
on Malfoy, Malfoy broke Harry's nose and threw the IC over Harry. 
Tonks found Harry under it before the train left.

So, no, DD didn't take the cloak from Harry at Slughorn's.

Eddie