I've been using 64-bit operating systems since right around when the 64-bit edition of Windows XP was released. XP seemed to have a bunch of driver issues initially, but they were sorted out as time passed by and hardware manufacturers realized more people were using the software (and, thus, started making drivers). I also have been using 64-bit Vista since well before Beta 1 was released, and that was pretty good with compatibility as well. I then moved to 64-bit Windows 7 ever since the builds were available, and again I'm fully impressed.
I've only had a few random compatibility issues I couldn't easily work my way around (one of which was a 16-bit console application given to us by a professor as an example for our assignment, but a quick install of DOSBox fixed that issue; another is that Alcohol 52/120% and DAEMON Tools don't yet work in 64-bit Windows 7 due to the wraparound SCSI driver not yet supporting the new operating system, but PowerISO achieves the same effect) but overall have loved using these operating systems. Anything not natively 64-bit runs just as fast as in 32-bit Windows, and 64-bit applications are accelerated for extra performance.
The reason you haven't heard anything about Vista is because most people have no idea what they're talking about (no offense to anyone here). When it first came out, the internet exploded with stories about how it ran horribly, or took up too much RAM, or whatever other excuse you've probably heard. That's because XP was able to run on antiquated hardware and be slimmed down even more to the point that it could practically run on a wristwatch. With modern hardware, Vista runs equivalent to or better than XP, and Windows 7 seems to run even better than that. Vista uses RAM efficiently, with a process called SuperFetch that loads the most commonly used programs into RAM to accelerate loading them when the time comes to do so. It only takes a nanosecond or two to clear the RAM for whatever needs it, such as your favorite game, so it's not degrading to performance at all.
or if you wanted to run more than 3.25GiB of memory.
Not entirely true, but close. 32-bit operating systems can only access a total of 4GB of RAM, which includes the system RAM, VRAM on graphics cards, cache in hard drives, XRAM on sound cards, etc. So once you calculate how much RAM is taken up by other things (GPU, sound card, etc.) you get the total amount of system RAM you're able to access. Processors from the Pentium Pro onward allow for PAE, or physical address extension, which sets some extra bits to allow for a total of 64GB RAM, but consumer versions of Windows disallow this for driver compatibility issues.
