New IBM AIX 5L ver 5.1 .. any thoughts?

I read that IBM came up with a new AIX version that would be fully integrated with Linux (I guess compared to older versions of AIX that could not) and I was hoping I bring this for discussion here so I learn more about IBM UNIX OS

Can anybody put few simple and practical comparisons between AIX, HP-UX and Sun Solaris (nothing too technical or fancy, just simple issues if possible)

To read about the new AIX go to:

http://www-1.ibm.com/servers/aix/os/51spec.html