In my eyes, 64 bit is the way of the future. That doesn't necessarily mean you have to jump ship and go to 64 bit right now, but moving forward, keep this in mind. More and more apps are demanding more and more RAM, and the biggest advantage of having a 64 bit system vs a 32 bit OS is that you can actually take advantage of additional RAM (I forget the exact amount, but 32 bit OS's can only see up to like 3.8 GB's of RAM, so if you have 4 GB or more installed on a 32 bit OS, you won't even be using all of it...)
Having tested the 64 bit version of each version of Windows since XP, I can say this: Xp Pro 64 is garbage. Vista 64 is ok, and Windows 7 64 is actually VERY VERY nice.
When I first starting using 64 bit OS's, it was hard to find drivers and apps that would work properly, but that is not the case anymore. Since upgrading to Windows 7 64, I have not found a single device or application that does not work just fine on my system, and many of these apps were not even designed with 64 bit in mind, and in fact, this was the case with Vista 64 as well.
One thing to keep in mind though, is that you cannot upgrade directly from a 32 bit OS to 64 bit. You will have to back up your data and do a clean install (which in my opinion is the best way to go anyway, but I know some really like using the migration wizard for the sake of convenience...)
So I guess my opinion on the matter is this: as someone who works with computers for a living, and someone that demands quite a bit of performance both at work and at home, 64 bit is the only way to go. I guarantee you I will never install a 32 bit OS again: having a solid 64 bit OS like Windows 7 on a machine that is properly built to handle it is nothing short of amazing. If you are not a "power" user though, I wouldn't worry too much about upgrading just yet. For most people, regular ol' Windows XP is more than adequate, and will likely be supported for a few more years yet by developers due to a massive user base. That said, I WOULD recommend going ahead and getting a 64 bit OS and the faster hardware for a little extra dough if you are buying a new computer anyway just to future proof it. A good rule of thumb is look at the minimum specs and double that and you should be good for at least a few years.