How safe/secure is this site?

The site is as secure as other comparable sites on the web. Plus, you only have to provide whatever information you're comfortable with providing. Some people include lots of background information on their profile, whereas others don't put much at all on their profile. In general, the more information you share about yourself, the more others will trust who you are and will interact with you (and therefore, the more helpful the website might be to you). You're also welcome to use the privacy settings to control what profile information can be seen, and who can see your information.

This site is just as safe and secure as any other site on the internet. Yes be careful

Well, it doesn't ask for your Social Security or driver's license number or address. Really only generic information that would make it hard to make heads or tails out of what is available (in my opinion). As LTC Kevin B. said, you only need to provide what you want.