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When I re-installed Lion on my newly purchased MBA, it said it would check some information by sending my Notebooks info to Apple to check if I'm allowed to load Lion.

So I was guessing that there could be a limit.

(I'm talking about re-installing the pre-installed version of Lion, not the App Store upgrade version.)
 
I take that more as verifying your notebook can run lion, than how many times you installed it.
 
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