First, it breaks a lot of existing functionality that I use all the time. How am I supposed to specify a search like +"Google's arrogance" now? You see, the plus sign actually did something different from just specifying that the word(s) appear exactly as written. It specified that all pages returned *must* include that term exactly as written. This might seem obscure to 90% of Google users but to the 10% who are power users it's a big time saver.
Second, it makes us type twice as many characters. This may not seem like a big deal if you work in a job in which you perform a Google search every few weeks, like marketing executives. But if you work in a job where you execute dozens of Google searches a day, it's a pain. And it makes one-armed searching maddening (which I do end up having to do frequently when I'm holding one of my kids on my lap or talking on the phone).
Finally, it tells me that Google is not serious about preserving backwards compatibility. This is a big deal. The next time I think about giving a conference presentation to my colleagues on power searching, I'll likely base it on another search engine with a more stable API (and one that permits wildcard searches inside words like Google used to do).