i successed to compile the mysql driver for qt4.8.1 with mingw and it work for me very good ^^, i hope for you too.
this a link to the qsqlmysql4.qll, qsqlmysqld4.qll, http://www.mediafire.com/download.php?z1e1ypqhqc96icn.
just to tell you, i compile under windows 7 64 bits, mysql-5.5.25a-win32.
after downloading this two dll files copy them to you sqldrivers folder (for me is :C:\QtSDK\Desktop\Qt\4.8.1\mingw\plugins\sqldrivers) then copy the libsql.dll ( you find it in your mysql's lib directory for me is : C:\MYSQL\lib), and paste it in your project directory, and it will work , well i hope so because it work for me like this ^^