Mac OS X Snow Leopard is first the entirely 64-bit OS for Mac. That is to say, the operating system itself has nothing whatsoever that is 32-bit.
But Mac OS X has been able to run 64-bit code for many years with all the benefits, depending upon the hardware on which it is run. This started the day the G5 PowerMac was released in June of 2003. This is very useful information to have at the ready the next time an Apple-hater questions when Mac OS X went 64-bit. Also point out to haters that all consumer level PCs are sold, by default, with 32-bit Windows installed, NOT 64-bit Windows. However, ALL Macs are sold 64-bit, period. There are no 32-bit Macs.
All Mac hardware went 64-bit in September 2006 when the Mac Mini Core Solo was discontinued. Be sure to ask any hater when IBM derived PC hardware went entirely 64-bit. You'll drive them insane. The answer: NEVER. At this moment in time there is no foreseeable date will all PCs will be 64-bit.
So what ships with Mac OS X Snow Leopard that is still 32-bit? Not much. I went through every application and here is what I found:
1) QuickTime 7.x, if you custom install it. QuickTime X is 64-bit.
2) iTunes. This includes updating to iTunes 9.0.
3) DVD Player 5.2.
4) X11 2.3.4.
5) Podcast Capture 2.0.
6) Grapher 2.1.
The end. Let me know if you find other stragglers.
There are a couple easy GUI ways you can tell what mode is being used:
a) Do a Get Info on an app and see if there is a check box for 'Open in 32-bit mode'. If there is, the app is 64-bit by default.
b) Run the app and check it in Activity Monitor. Look in the 'Kind' column. If the Kind says only 'Intel' then it is running as 32-Bit. Otherwise it would say 'Intel (64 bit).
One very kewl thing about Mac OS X is that the kernel runs 32-bit processes NATIVELY. However, 64-bit Windows has to run 32-bit processes in emulation. That means they run more slowly than they do in 32-bit Windows. Emulation speeds suck compared to native speed. Your haters won't like that either.
Then of course finish your 'mine is bigger than yours' contest by pointing out that Macs are capable of running both 32-Bit and 64-bit Windows natively at faster speeds than PCs. (Google it for yourself to verify). Then suggest, in a friendly manner, that they defect from the PC and Get A Mac. Statistics consistently prove that they will be happier when they switch to their 64-bit Mac.