It depends on how ads are blocked by the user, and it also depends on how you frame it. For example: I don't block advertising on Something Awful, because the ads there are both unobtrusive and occasionally quite relevant or interesting to me, even in terms of pointing me at things I didn't realize I had an interest in. I'll also usually unblock sites that detect that I'm running an adblocker and ask me politely to stop.

I will, however, make a point of blocking ads on any site that decides to drop full-screen overlays, modal dialogs, javascript popovers, or any of that other crap that ad agencies seem to love these days. If your ad is interfering with my browsing experience, I'm not going to waste my time even considering interacting with it.