The site notes that the development kit "isn't the console's final form factor" -- and then, in an update, mentions that, according to a source, Sony has already replaced this version of the dev hardware with a non-sliding version, designed to rectify an overheating problem. Which means that even if this thing is real (and we're not at all convinced it is, considering, for example, that it lacks the distinctive segmented PlayStation D-pad), it doesn't look anything like whatever the final hardware will be.
[Update 5:15pm ET: We've got some more truth gasoline to add to this rumor fire ... or something. After running the images, IGN updated its post with the following: "A development source confirmed to IGN these photos are legitimate." So, best case scenario: this is what the PSP2 dev kit looks like and a rough idea of its feature set, though the hardware (including the PSP Go-style slider) is still at the prototype phase. Either that or both VG247 and IGN's sources are wrong.]