I have a general question here..
There are various sites which offers ready made scripts to fit into users requirement. Is it safe to download and use them in our projects directly.
I have downloaded content from http://www.menucool.com/.
I think most (if not all) sites that provide independently written scripts have disqualifying statements indicating that the site owner cannot be held responsible if a script written by someone does damage. That's pretty much standard operating procedure.
That said, it really comes down to the reputation of the site in question. I've never been to menucool, so can't speak as to reliability or safety. I'd do what you're doing - asking around to get feedback on a particular site.
A good indicator of a well written script is that the entire script is in a separate file that can be attached at the bottom of your page and will only require the insertion of one or more ids and classes into the HTML in order for it to work.
If you're going to use an external script/library/framework, there are security implications to consider, especially if any of it sends data back to the server (ajax calls, form posts, etc). This applies to any code you're using, not just JS. Make sure you keep up to date with any external code you're using (typically new versions come with performance and security improvements).
Nothing on link, a broken one..
Sorry. I have fixed it now.