all three OSs r perfectly usable. no lag issues at all.
i hav been using osx mostly in the last few weeks and i am very impressed with its speed. i have itunes running at logon and it have it running continuously in one of the other spaces. the animation from one space to another is smooth. also have firefox instance running in the primary space usually with numerous tabs open and still everything is snappy. i'd say osX seems to be quicker/equal to xp's speed except for the 50seconds that osx takes for booting.
but getting osx to work took a lot of work(much much more than the other two) starting with ideneb 10.5.5 and numerous kexts to fix everything thats broke after the installed. but it was well worth the effort.
i have ubuntu hardy heron installed with a customized kernel made for 1000h which made everything work out of the box. at present i have left the ui of hardy uncustomised, but compiz is still running. i had earlier in another installation of hardy a fully composited desktop with the desktop cube, minimize maximize animation, a osx like dock. but right now i m using os x most of the time so hav not spent time customising the ubuntu installation.
windows is also a modified version with lots of unnecessary things removed to make the install smaller and faster.
booting is handled by ubuntu's grub which for osx then initiates chameleon - the bootloader for os x.
the partitions are as follows-
windows-17gb
osx - 40 gb
hardy - 22gb
+1gb swap
installation order was
1st- osx
2nd- ubuntu
3rd - windows
and then created another partition to hook up to ubuntu as swap space, since windows wont install if 3 partitions are already present.
at last i fixed the grub menu with ubuntu's live cd .then booted into ubuntu to figure out the entries for the other oses.
a few litres of coffee and 10%loss of vision in my eyes reading howtos and forum posts online went into making my 1000h the ultimate os junkie's toy.
i will try to post a mini howto later with links to posts i followed to install each os
