You will probably need to http://www.sevenforums.com/tutorials/18715-activate-windows-7-phone.html on subsequent installs, particularly if they are on different systems. Be aware that only 1 system can be activated at any time with a single key, and that any previous systems with that key must have the OS removed from them. Should you omit to do this, and an occasion occurs where more than one system using the same key is online at the same time, you run the risk of having the key black-listed, in which case it will no longer work.
My Computer
At a glance
Windows 8.1 Pro RTM x64Intel Core-i5-3570K 4-core @ 3.4GHz (Ivy Brid...4 x 4GB DDR3-1600 Corsair Vengeance CMZ8GX3M2...MSI GeForce GTX770 Gaming OC 2GB
4 x 4GB DDR3-1600 Corsair Vengeance CMZ8GX3M2A1600C9B (16GB)
Graphics Card(s)
MSI GeForce GTX770 Gaming OC 2GB
Sound Card
Realtek High Definition on board solution (ALC 898)
Monitor(s) Displays
ViewSonic VA1912w Widescreen (VGA)
Screen Resolution
1440x900
Hard Drives
OCZ Agility 3 SSD 120GB SATA III x2 (RAID 0)
Samsung HD501LJ 500GB SATA II x2
Hitachi HDS721010CLA332 1TB SATA II
Iomega 1.5TB Ext USB 2.0
WD 2.0TB Ext USB 3.0