Doing a simple Google search shows that there are many places on the Internet that say that they give out free bitcoins. All you need to do is give them your deposit address and confirm that you're not a robot, and boom, free bitcoins!
Do "faucets" like this really work, or are they scammers?
Faucets like that really exist and work, however, there probably are also some fakes. Nothing can be done with a Bitcoin address except to use it as a recipient address and/or see the transaction and balance history of the address.
E-mail addresses are not required to send bitcoins. Unless you can discern another legit reason for them needing the email address, it seems more likely that they are collecting the email addresses for other purposes, such as advertisement, phishing attacks, or to glean addresses related to online wallet services.
I'd be careful to check whether such a faucet service is actually connected to some legit operation. It would probably be a good idea to use an email address especially created for that single use.
Also, be aware that today most faucets only give out minuscule amounts of bitcoin, usually not worth your time and effort. If you can find work for the invested time instead, you can probably buy a multiple of the bitcoins with the earned money instead.
There is no danger in providing your Bitcoin address.
For sites that use inputs.io, certainly you have to provide some way for them to know which account to credit. The security of that account depends on the strength of your password, and how much you trust inputs.io.
A more fundamental problem with these faucets is that they are a complete waste of time. The ones I've seen offer .00001 BTC for looking at an ad, solving a captcha, and entering your account info. This takes 30 to 60 seconds. At current exchange rates that is roughly 10 US cents per hour, about 2 percent of minimum wage, for perhaps the most boring work I can imagine.
It's also not a good way to just pick up a few satoshis to start playing with the system, because thanks to aggregators like inputs.io, you typically cannot get your coins until you have earned BTC .0005 or so, which would take about an hour. Totally not worth it.
In short, I think if it were a scam, they should be offering much better bait.
Most faucets are based on ad revenue. Bitcoin fauces do give aways fractions of bitcoins for you to visit sites filled with ads and the faucet collects revenue when you visit the site. To prevent bots from doing the work there's often a CAPTCHA on site the for you to prove that you are human.
The faucets have often have a small fixed amount of BTC to give away and obviously they want to be running for as long as possible to collect ad-clicks. To do that the BTC giveaways are minimal, and they are alwasy smaller than what the faucet collects form the clicks.
I wouldn't call them a scam, but they do profit more than you do.
