Upgrading an OS on an existing system is more problematic than buying a new system with the OS already installed. New versions of an OS often have compatability problems with old drivers and manufacturers don't always release new drivers in a timely fashion, if at all for older hardware and software. 

Most people buy a new computer every three or four years, so it's usually best to wait for a complete system upgrade (which will include the cost of the new OS). Depending on what kind of computer a person wants to buy, anywhere from 10%-30% of the cost of the new system will be wasted on upgrading to W7 today. Based on Microsoft's past OS releases, early adopters will be advanced beta testers.

My advice would be to save the money and buy a new computer in a year or so, with W7 installed, after it's been patched up with a couple new service releases.

As far as XP going away, that won't happen till the bulk of new netbooks have migrated to W7.  Netbooks gave XP an extended stay of execution. Microsoft wasn't about to let Linux be the primary operating system on a new class of computers. Microsoft initially offered Linux netbook users a $25 upgrade path when the normal XP upgrade was over $100. Microsoft is competitive when they have to be and not competitive when they don't nee

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