It's free money. No one hates free money.
I've used Google Opinion Rewards since it first came to the UK, but my appreciation for the service has grown exponentially in recent months, as has the number of surveys to fill out. It's now at a point where I'm comfortable in saying it's one the very first apps I'd recommend a new Android user downloads.
If you can get it, there's absolutely zero reason not to.
Google Opinion Rewards is basically a market research tool that Google will pay you to use. In exchange for answers to the surveys it provides, Google will give you varying amounts of credit to spend in the Play Store on any content available within. Surveys in Opinion Rewards are typically created by outside researchers for academic and commercial use, and unless otherwise stated up front your answers are anonymously aggregated and passed on to the researchers.
Most surveys are fairly brief, and by answering a few quick questions every so often you can quickly build up a sizeable credit.
Of course, the frequency of surveys and how much they pay out will vary depending on location, but at least where I am they've been coming thick and fast of late. At least one or two a day it seems come through asking for basic information on shopping habits based on my location history (which I'm OK with sharing.) My current balance stands at over £9, which is great, because I didn't really do anything. It's free money which I get to spend on content to enjoy with my son.
So, if you're new to Android, or just haven't come across this app yet, do yourself a favor and download it. You can't say no to free, really.