I have to agree with the above posters. The Prophecies guide was based on a beta version of the game, so it wasn't even accurate when the game first came out, never mind a month or a year later. The skill descriptions are horribly out of date, the mission guides are vague to the point of uselessness, and the appendices are so full of misinformation you have to wonder just what beta version they were based on.
The Factions guide was a little cleaner (plus it had a nice beefy lore section), but the same complaints remain. The mission guides are even worse than in Prophecies (with maybe 1 paragraph of useful info), and the skill and item lists are similarly out of date.
One of the few good things about the guides were the maps, both the individual area maps in the guide and the poster maps (I currently have both hanging on my wall). However, any fansite worth its salt will have a maps section, and we got a Nightfall map in the CE (smaller than the Prima maps, unfortunately), so I'm not complaining.
I'm glad ANet figured out how useless the things were- why make people pay for a printed guide, when they have a loyal army of fans willing to compile this information for free on fansites which are a hundred times more complete and updated within hours of a new build going live? (Of course, I think the fact that past sales were poor due to most people using those online fansites instead of the Prima guides in the first place had something to do with it as well

)