While rumors abounded earlier this week of a revised version of the PSP that would be lighter, it seems those rumors are false. A UK Exec for Sony has come out to say that they have no intentions or plans to revise the PSP in such a manner. The rumors started from a statement last week from the company that made it sound like it was possible, though now they have stated it was misinterpreted:

“If you're referring to what was reported some weeks ago, I was referring to the fact that that's what we do as a company,” said Maguire. “We R&D everything. You only have to look at PlayStation and PlayStation 2 to see that's always in our mind.”
As the article mentions, handheld redesigns have often led to surges in sales. Given that, it won't be a surprise if Sony does work on a revised version, but the weight of the unit is obviously not a priority.