I purchased a G5 Mac when they first came out, and like you, I really hated that computer, I gave it away after 3 months. After using XP and Vista (I actually liked Vista) for a few years, I really got tired of all PCs looking the same, so I got a MacBook Air with Leopard on it, and I actually liked it - it was so much better than that G5 that had made me hate Mac's. After being happy with that I slowly started migrating my business to all Mac's. I don't hate Windows at all though, I do prefer OS X now, but as an IT Analyst still depend on Windows for SharePoint related tasks.
If you have the hardware, a 64-bit OS takes better advantage of RAM, so it allows you to have more than 4GB on your computer. Running 64 bit software with a 64 bit compatible OS means that the CPU can process more data per clock cycle too. The average user may not notice a difference, but with technology becoming more memory and graphic intensive, many may see a need to eventually run 64 bit compatible hardware and software. ...that years from now though.
If you own a new computer, which has 8GB of RAM (optional upgrade) and a Solid State drive, and virtualize to run other operating systems, or run demanding software (like multiple Adobe CS5 products at once), than it makes sense to take advantage of the hardware by using a 64 bit OS.