The site claims that the current Penryn chips can't be overclocked by more than 10 percent:
The 3 GHz core will run at up to an additional 300 MHz and that's about it. Intel is expecting the next revision of the Penryn core within the next few weeks and this one is supposed to reach the sky, as its 45 nanometre and has significantly lower heat dissipation than Kentsfield.
Intel is doing fine since it doesn’t plan to launch any desktop variants of the 45 nanometre Penryn until Q4. This core is certainly in better shape than AMD's Barcelona.