Bear in mind that Google might be correctly identifying your IP address as a botnet source. If you start seeing lots of CAPTCHAs, it's worth it to take a look around your network for open ports or weak ssh passwords etc., or just look at a traffic monitor to see if there's a lot of egress from your net.
Oh, I'm sure there are a million reasons for them to block me. I normally use a VPN, incognito searches, limited script blocking, and cookie blocking. Pretty sure they don't want me as a customer, not that I can completely blame them. Anyway, I've discovered that there are other reasonably effective search engines with a different business model, and I'm fine using those and giving them a modest amount of revenue. (I don't block ads that don't track me.)
