When choosing a back-up service provider, here are some issues to consider:

1. Do you have special security needs involving regulated data? If you have medical, financial, educational or other sensitive files, what security and encryption protocols are available for your protection?
2. Where, exactly, is the data being stored? Potentially, the location of the back-up can be anywhere in the world, including sites outside the country where you live. How safe is your data if it is located beyond your borders?
3. How long will it take to get your data back, if needed, from the back-up provider? Remember: large sets of data may take many hours to download via the Internet. Is the service accessible 24/7?
4. Is the back-up service a viable business that will be around for as long as you need them? During the last economic downturn, several data storage firms went belly up and left customers in the lurch without access to their files

In what appeared to be a hasty response to the launch of Google‘s rival social-networking product, called Google+, Mr. Zuckerberg on Wednesday unveiled Facebook’s new video-chatting feature. He called it “super awesome.” Too bad Google made the same feature available in 2008.

Indeed, Facebook suddenly looks vulnerable. This could be bad news for investors who have recently paid top dollar for stock in Facebook in private sales.

Rule No. 1 when launching a social network: Make everyone wait in line. Exclusivity was how, in its early days, Facebook built buzz. For more than two years, you couldn’t get in unless you had an email address ending in .edu. Google is using a similar strategy with Google+.

Facebook should take note: Google used the strategy before to kneecap Yahoo in all-important email. For a long time, the bulk of Yahoo’s traffic was driven by users dropping by to check their Yahoo email. Then Google rolled out Gmail—but only by invitation at first.

Rule No. 2 is to deliver a better service. Adopting a new social network could prove similar to adopting a new email address: Many will try it out, but to keep using it, they have got to be given good reason. That Gmail offered significantly more storage space than typical Web mail meant millions were willing to make the switch. Similarly, Google+ offers upgrades on what many perceive to be Facebook’s shortcomings.

For starters, Google+ gives users a handy way to organize their social contacts into different “circles”—friends, relatives, colleagues, etc.—with which they can share appropriate things. Though Facebook now offers the option to create “Groups,” users broadcast their information to everyone by default.

Google+ also offers group video chats. That is why Facebook’s announcement of one-on-one video on Wednesday seemed to fall short. Facebook has yet to introduce group video chat.

The biggest hurdle for Google+ is getting users, of course. But it is integrating the service with Gmail, which already has 240 million unique users worldwide, according to comScore.

Meanwhile, the user experience on Facebook is a victim of the site’s success. Users have accumulated so many online “friends” it can be difficult to organize them. And users often feel assaulted by too much or irrelevant social information, like Zynga game updates. Utlimately, Google+ is a chance for social networkers to start over.

This doesn’t mean people will drop out of Facebook overnight. Gmail users didn’t necessarily drop their Yahoo email addresses. Indeed, Yahoo Mail still has more unique visitors, but its growth has been stagnant, whereas Gmail continues to expand quickly.

Facebook is already showing the first signs of slowing growth. One research firm, Inside Network, recently reported that Facebook’s U.S. users dropped six million to 149 million during May.

Add it all up, and Google+ looks like it will keep Facebook on the defensive.