+1 to BlueWeasel.
If you physically bought 1 copy of Windows 7 Ultimate, you get one key. You can't expect to be able to install that copy onto multiple machines at the same time. Technet keys are no different. They just bypass the physical media (getting the DVDs is extra charge) and you just download the ISO's. Then you burn your own DVD, or make a bootable USB key.
Do ALL of your PC's really need to have Win7 Ultimate on them?
Just spread out the versions you have - 2x Ultimate, 2x Professional, 2x Home Premium, 2x Basic (lol, don't bother with this unless you're desperate), then the various "N" versions.
Also, I believe all accounts also come with a single Enterprise edition key, which is a VLK - Volume License. You get only one key, but it can be activated 100 times (I think simultaneously?)
*Someone correct me if I'm wrong; I don't know if this VLK only comes with the Professional account or not.
What makes Technet so much more attractive is that you're not limited to just Win7. You get Vista, XP, 2k, etc, as well as first crack at new stuff, such as Win8 RTM. You ALSO get 2 keys for each Microsoft Office product, and many other software. Again, not *technically* for production/home use, but that hasn't stopped anyone.