MSI's dual-storage Wind U115 Hybrid netbook was advertised as not only a speed demon (thanks to the 8GB or 16GB SSD) but a frugal one, with the company predicting runtimes of up to 10.5hrs from a single charge. However it now looks as though MSI were actually too modest in their claims; Eee PC.de have been running battery tests and the MSI Wind U115 lasted 13 hours and 15 minutes.
The test was run in Battery Eater Classic, which continuously calculates the decimals of Pi until the CPU is at 100-percent, as well as running 3D graphics tests. As for netbook settings, the U115 was switched to 30-percent brightness, using SSD only (rather than the HDD) and WiFi turned off; we're promised a second batch of testing with the WiFi on, but considering it's unlikely you'll be constantly stressing the CPU to 100-percent in daily use the wireless is unlikely to make too much a difference in the real-world.
Runtime like that is not only a full work day but potentially a full day full-stop, considering you're unlikely to be using the netbook every moment. The standard battery is a 5,200mAh unit, and you'd have to be content with just using the SSD rather than making the most of the also-present 120GB or 160GB hard-drive, but many won't see that as too great a hardship.