Niner since 2009
I use a HP 2710p convertible tablet PC with 4Gb and W7 x64.
The small screen isn't ideal for development but in slate mode it's perfect for taking notes in meetings and drawing out diagrams.
With the 2nd slim-line battery it'll easily run for 7 hours without having to switch off radio and dim the screen.
Shame it doesn't support multi-touch though :¬[