Ive gone with Game and put my £20 down, I got the 360 on launch day from Amazon, however they messed so many peoples orders up... i feel that i got lucky to get mine when i did.
£300 would be the sweet spot for me (or less) it will certainly harm sales if the console is much more i think. One of the reasons the 360 dominated the PS3 was it landed early, was around £150 cheaper and did most things better.
Even though the Xbox is now firmly established as a console i hope Microsoft don't get complacent.
Think I'll be keeping my 360 for a while yet I like the look of the console but I waited almost a year for my first 360 and I can wait again for the Xbox 1.