But is this term even relevant for the actual end user? First of all: GitHub in it's current state doesn't seem to have ads anywhere. At least I couldn't find any and I allow GitHub to send me ads (apart from the "ad" for the hosting company). Then there is also the part, where they have to try to detect whether you're blocking their ads or not. Not impossible, but also not all that easy since I guess you'd need the server logs from both: GitHub and the ad-provider.
Also: If a site like GitHub or any site for that matter has more ads than content and therefor the content is no longer all that relevant, do you really want to be there?
I guess it boils down the problem, that some people simply don't seem to understand, that if a company offers something "for free", they have to make the money back somehow. If the free plan should be usable, you have to calculate with many people using it and never upgrading to one of the paid plans. In those situations advertising is more or less the only way.
It's not really a question about if this term can be enforced, but more about if you as a customer like a product. If you like it, you want to use it. If you want to keep using it, you better help the company to stay in business.
On the other hand advertisers naturally know about ad-blockers and I guess -- as defunkt stated in that discussion -- such a clause shows them, that the company cares about them too.
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