There are probably several other types, my favorite being those who don't know, claim to know, and by total fluke of luck, get it mostly right
Those that pass uninformed speculation off as fact are unhelpful to say the least. Those that brag "I know but I can't tell you - na na na na na" aren't much helpful either unless there are words to read between the lines (and there often are). If Apple rumors are any indication there are those that are embedded in the industry with lots of contacts yet no formal NDAs to follow. When they create rumors or "well informed predictions" that are proven to be 95% accurate then that's something worth watching.
On rare occasions, manufacturers intentionally leak out information via well places sources that are or aren't under NDA. This can help create a "buzz" and prevent users from buying a competitors newly announced product until their product announcement comes out, for example. Sometimes large sales channels are told by the manufacturer that supplies of an older product won't be replenished or that a new product will arrive on a certain date and it's pretty obvious what they're talking about.
I know first hand that it can be very frustrating to have an NDA and hold your tongue while others talk about a product they've obviously gotten some intimate experience with. When you've spent the time contributing to product testing via the right channels you kinda expect to be a knowledgeable person people look to when the right time comes.
So I don't think it's as black and white as those with an NDA know and everyone else doesn't. Either way, I wouldn't expect to see much insight here in such a public forum.
