The Dutch website PS3Life.nl highlights an unofficial rumour that made the rounds in October of this year.
After the relatively unexpected Uncharted 2 reveal, what kind of joys might be met by the announcement of Jak IV. One website hones in on a shaky statement.
However reliable the source might be, there's no way Jak IV will be announced for the PlayStation 3, since Naughty Dog are head deep in Uncharted 2: Among Thieves development.
If anything, there might be a Jak and Daxter release on the PSP, in a similar vein to Resistance Retribution, which was not developed by the series' PlayStation 3 developer Insomniac, but by Bend Studios.