1) When not running as an administrator, the restrictive nature of the Program Files directory makes it very difficult for an Eclipse based application like MyEclipse to work – especially when it comes to simply updating to a newer version of MyEclipse or adding/remove new plugins from your installation.
2) We strive to maintain a consistent user experience so having one installation directory when you are running as administrator but another if you are running as a non-admin user is something we would like to avoid.
3) The AppData\Local folder is a per user location that is not shared between users or on a network. You could have multiple users on the same machine have their own customized versions of MyEclipse (or other Eclipse based installations where Pulse is concerned) without having to deal with the fact that the same installation will be used by other users too. As far as it being hidden is concerned, I agree – though typically other than the management of “drop-in” plugins, you would be managing your configuration from the MyEclipse Configuration Center and shouldn’t need to worry about the installation location.
For a quick example of other apps that do this – Google Chrome will install its binaries inside AppData\Local as well.
Of course, you are free to install to any other directory as long as you have the rights required to write to that location – e.g. c:\ide\MyEclipse would work just fine as well. However, if you already have an existing MyEclipse installation, then this installer will reuse the resources of that installation and you may not be allowed to install elsewhere – for example, the Common folder where the binary bits are usually installed will be reused and new bits will be added to that location.
Please let me know if you have further questions or thoughts.