Reportedly clocked at only 600MHz, the "Ultra Low Voltage Celeron A" lacks the SpeedStep technology found in Intel's other mobile processors. In typical Celeron fashion, the chip also features half of the Pentium M's 1MB cache. With much lower clock speeds and less cache than Intel's Pentium M, it's unlikely that these new Celerons will have much to offer in the performance department. However, given their apparent target market, they may only need to offer better performance than VIA's C3 and Transmeta's Crusoe processors.
Honestly, the thought of a really light, really small, and really cheap sub-notebook based on a Celeron version of the Pentium M is appealing to me. I already have a speedy, beefy, high-powered notebook to handle my mobile workstation needs, but a cheap ultra-light coupled with a home WiFi network would be great for emailing from bed, posting in the forums from the yard, and surfing the web from, um, never mind.