Our Acer Aspire One D257 netbook had an odd issue where it would simply freeze when any sort of load was put on the wireless network (for instance, when downloading files). There is a dearth of information about the issue online; some people blamed the wireless drivers, some thought it was overheating.
One bright spark managed to track down the problem - a bad BIOS. Flashing it to a later version (in my case from v1.08 to v1.15) fixed the problem immediately, so I'm posting this resolution here in case anyone else has a similar problem.
The BIOS update file is on Acer's site:
Just in case it gets removed, there's a copy available here.
Hopefully this will be of some use to someone!