"How many computers you've had since P4?"

Just one, but like the cells in the human body, its components periodically slough off and are replaced with young, vigorous ones. :-) My main rig can trace its history back eleven years, but literally everything in it has been replaced at least once, including the case--and some things have been replaced several times. It started life as a 33 MHz 386 with 4MB of RAM and 120MB of hard disk space; now's it's an Athlon XP 1700+ with 1GB of RAM and 100 GB of hard disk space. Ahhh, progress. :-)