Actually, this is how it works,
You get 10 keys and each key gets 10 activations. when you run out of keys and activations you can request more keys, if your Technet Subscription is still active.
If i remember right, keys from msdn/technet got 10 activations or something? So am wondering if i want to reinstall windows 7 with the same key, on the same hardware, will i use up another activation on that?
Yes, you will use another activation.
Here is from the
FAQ:
Q: Can I determine how many activations are remaining for my keys, if activation is required?
A: No. When a Microsoft product requires activation (such as Windows Vista), the product keys provided with your subscription allow a limited number of activations. The product keys available through your subscription can have one or more activations per product key. Multiple Activation Keys for older products typically are 10 activation keys. As subscribers often have legitimate needs to install and reinstall software more often, we are working to increase activations available for keys,
or to enable issuance of additional keys. Going forward we plan to continue to support this business need and increase the number of activations for subscribers, or enable multiple keys to be claimed.
IMPORTANT - If you use products that require activation, many allow up to 30 days usage without activating. If you re-image your computers more frequently than every 30 days, you may want to consider NOT activating them if you have that option based on the product you are installing.
If you deplete activations for a key, you may be able to claim additional keys for that product. Additional keys would have their own set of activations.
If you are unable to claim additional keys and you have depleted all activations on ALL keys claimed, you can request additional keys by contacting your local Customer Service Center (click the Support tab above). A Customer Service Representative will validate your request and will submit the request to have additional keys provisioned for you. The additional keys will be claimable from the site.