I love the philosophy of just taking money from users and working on giving them what they want and having nobody else to answer to, and I think the results from that philosophy have been excellent. But my biggest (only) complaints are difficult to solve for a paid search engine that requires login.
First, sometimes I end up logged out. And maybe I've changed my password in the meantime and it's not saved on the machine I'm logged out on. It is supremely frustrating to search for something and be met with a login screen instead, and enraging if I can't immediately solve it by logging in.
I'm hopeful that I can actually just search logged out now if this happens, and log in after I'm done with what I was doing.
The second is the requirement to install a browser extension in order to search from the unified search/url bar. I really wish browser vendors -- or, well, Apple is the only one I care about -- would support it directly.
I think they don't want to support a search engine that requires an account. It would be cool if the 100 free searches is progress in this direction but I'm not sure if it will be.