HBP: Chapter 3 - Will and Won't

We are reminded several times to be aware of Death Eaters "masquerading as others by use of the Polyjuice Potion." (42) And the Ministy's flier encourages people to come up with security questions but we rarely see them used. We know Draco was using Polyjuice Potion on Crabbe and Goyle but are they the only ones? I highly doubt it. Who else isn't what they appear to be?

We are also warned to keep an eye out for strange behavior related to people being under the influence of an Imperius Curse. We already know of one victim of a failed Imperius Curse anyone else out there not in control of their behavior?

Dumbledore has always had an odd sense of humor but he seems a little meaner than usual (eventhough one could argue that the Durselys deserved it).

Dumbledore refers to his correspondence with Petunia. Harry finds the phrasing odd and Petunia shows no disagreement to the plural phrasing used by Dumbledore. How many times have they corresponded and what have they corresponded about?

Watch out for all the telescope references.

Dumbledore has no problem talking to Harry about private matters in front of the Dursleys (if fact it seems like he really wants them there) but in the next chapter he can not talk to Harry in front of the Weasleys. Odd...