Lenovo's decision to delay the Skylight smartbook wasn't exactly explained in any detail; the company merely confirmed that the expected April release has been pushed back to sometime in June 2010, giving them time to "finalize the product." According to DigiTimes, however, it's not just finalization they have in mind but reworking the smartbook to better compete against the iPad.
Their notebook sources reckon that Lenovo have got cold feet over the Skylight's smoothness and general performance, after deeming that it fell short against the iPad's browsing experience. No specifics, but given both devices prioritize web access while mobile, it seems likely that Lenovo are looking at things like rendering speed, website compatibility and other aspects. Of course, the Skylight potentially has more functionality than the iPad, helped no small amount by its physical keyboard, and it's possible that Lenovo are looking to make better use of its hardware advantages.