How to install Dropbox in Windows 7 for all user accounts

In a nutshell...

Install For All Users would be used when you want the program to be "active" for anyone who logs on to the computer with their personal account (if there is more than one login). A good example would be an antivirus program, that you would want to be available while any user is logged in.

Install for Current User is normally used under an Administrator account for something that handles disk operations and other admin-type functions, such as Acronis True Image, a keylogger (to track what non-admin users are doing while logged on), and other disk-related or sensitive software.

but in Ubuntu its usually stored in the users local directory.

Hmm. This isn't really true (or I misunderstood what you meant). Usually programs are installed using Ubuntu's package management system (deb packages), and they are available system-wide for all users. This is by far the preferred method of installing software.

When (on rare occasions) installing something outside the package management system, I tend to use /usr/local/programs, and create specific subfolders there for different programs. Often, I'll also put a symlink (or simple startup script) under /usr/local/bin to make it easier to launch these applications. Of course, /opt or any other location would do just as well, as long as you make sure all users can access the files and directories (as Bobby pointed out).

If you want such programs to appear in the start menu of your desktop environment, you'll need to take care of it yourself. E.g. this shows how to add entries (for one user?), assuming you use Gnome. I'm sure there's a way to add it for all users, but off the top of my head I'm not sure how; maybe others can help you there.