While trying to install Piwik I couldn't get past the System Check page. It was complaining that I didn't have the PDO, PDO_Mysql or MysqlI extensions.
I tracked this down to the core/piwik.php globr() function. The path being passed to it contained backslashes and the escapeshellcmd was removing them (replaced with spaces), thus making the path invalid and causing the system check to fail (when looking for db adapters).
I added a simple str_replace to change backslashes into forwardslashes and it works fine.
For easier compatibility there shouldn't be any need to use backslashes for Windows when in PHP (except for executing external applications which would then rely on normal windows paths).
duplicate: See patch in .