Microsoft will launch Windows 7 in October. A new Microsoft OS introduction is a major milestone for hardware makers. So if you are actually buying a Vista notebook or XP netbook this summer with the free Windows 7 upgrade you will actually be stuck with heavily outdated hardware.
What new netbooks and notebooks will be launched is still murky, but CNET has an interesting report from the Intel Technology Summit in San Francisco that took place last Wednesday with some details on what to expect in the new Windows 7 notebooks and netbooks.

According to Intel netbooks will see a major design overall with the new Intel Pine Trail Atom heavily integrated chip.
Intel's Pine Trail combines CPU and GPU in the same chip and will offer better performance.
Other new features of the new Windows 7 netbooks and notebooks will include thinner designs, better cooling and HUGI power-saving technology.

So my advice is to hang onto the hardware you have until the Windows 7 release rather than opting for the Windows 7 upgrade.