Yes, but this is not a good idea - I assume you are talking about backing up an entire user profile folder.. If you backup the entire folder it will also backup number of system files that could be OS dependent as well as being potentially locked too (like user registry hive). Those files could be incompatible between OS versions - for instance desktop.ini has changed from XP to Vista completely. There are other files that simply copying from one OS to another will not work. Outlook as classic example in terms of the worst registry settings design - every single version of Outlook on every single version of OS differs in storing its settings...
Generally it is better practice to capture individual application settings and user files, eg. $Documents$, $Music$, $Desktop$ etc. Of course you can use paths like $Profile$ (entire user folder) but I wouldnt recommend it for reasons stated above.