This tool is only interesting when after a fresh installation + servicepacks.
Tried it myself on an existing XP system (with 320GByte hard drive) and after 4 hours 4 of the 6 partitions were aligned. A result quite similar to hpierce, the previous poster.
I also tried it on a fresh installation (XP SP2), used the tool and all partitions were aligned. In my finite wisdom I installed SP3 and all appeared to go well. But after the mandatory reboot, a blue screen of death showed up and one reboot later the complete system was hosed. By that I mean the PC would loop through the POST of the BIOS, nothing more.
Reversing the order (installing XP SPII, updating to SPIII and then aligning partitions) looks to be the proper way of doing things.
It really does help, I always have Process explorer running in the tray and I noted that hard drive I/O improved. My existing XP system acts as an active Oracle XE database server and I note it there as well.
This is not a tool for the faint of heart, though.