1) I don't see why backups are any harder in the new configuration. The backup situation is in fact much better because now everything worthwhile is in your user directory so you're not backing up unnecessary files (ie. the mIRC exe and help files) and if you're creating a backup of all your programs' settings then you only need to backup your user dir, not your user dir plus a special exception for your mIRC installation directory.

2) Why would you need to install mIRC more than once anyway? mIRC's -r command line switch allows you to have a single mIRC installation from which you can run multiple instances each using separate settings and scripts.

3) It seems like a rare situation where you would need to temporarily install mIRC on somebody else's machine, an even rarer situation where you would be given administrator access to do that. I certainly don't see why any log files you left would be incriminating, sounds like maybe people shouldn't be giving you admin rights on their machines! As others have said though, there are already multiple solutions to this problem:
- Use the -portable switch
- Use the mirc.ini trick
- Use the -r command-line switch when you run mIRC
- Install mIRC to "%APPDATA%\mIRC" so there's only one location to delete


Spelling mistakes, grammatical errors, and stupid comments are intentional.