The Atheros AR5007EG in my NC10 netbook has been randomly dropping the wireless connection.
I would have to disable/enable the adaptor for it automatically re-connect.
Changed the driver to previous versions by 'Atheros Communications Inc.' and it still happened.
Changed the driver to the version labelled with 'Microsoft' and it was a lot more stable.
Also worth checking traffic in your area using InSSIDer (http://www.metageek.net/products/inssider)
With wireless routers being given away, you can suddenly have neighbours using the same channel.