This is a topic that is and has been debated to death on the
Ubuntu forums. I suggest you search there for "32-bit vs 64-bit" discussions.
The short story is this: if you want the "easiest" Ubuntu experience, go with the 32-bit version. Why? Things like Flash, wine, and other 32-bit apps will "just work". There are ways to get Flash, wine, and other 32-bit apps working in a 64-bit Ubuntu environment, but you'll have to find online resources with the installation instructions.
I run Feisty Fawn 64-bit native on my AMD Athlon64 3200+ based eMachines box at home. I am able to run the 32-bit version of Opera for Linux if I run a command line command to force the installation (the normal installation method won't work since the installer will report you're trying to install an app that doesn't match the OS native architecture), which is fine but I had to find that command before I could do the install. If I ran the 32-bit version of Ubuntu, I could just install the Opera installation file by double-clicking it.
I currently live mostly without Flash support in Firefox, Seamonkey, and Epiphany (GNOME's browser). If I absolutely have to have Flash support, I run the 32-bit Opera browser I have since 32-bit Flash works in it (for the most part).
I fully advocate and support running Linux 64-bit native since the more 64-bit users there are out there, the more software developers will port and develop 64-bit native apps. If you're ok with putting for a *little* bit of effort to get support for some 32-bit apps that just aren't available 64-bit native yet, go with the 64-bit installation. There are scripts and TONS of threads on the Ubuntu forum which will help you get the 32-bit apps you need working in your 64-bit Ubuntu installation.
Otherwise, go with the 32-bit version and see how the software trends develop in the 64-bit world.
I haven't had any issues with device drivers or stuff like that and I can connect my digital camera or other USB devices (like an external USB 2.0 HDD) to my machine and things tend to work as expected.
Good luck!
Peace...