Main difference I see in a practical sense is memory caps. 32 bit is limited to the old 2 GB threshhold without AWE and you have to use AWE (which to me is like loading device drivers high) to access physical memory greater than the OS limit. Whereas in 64bit SQL, you can pretty much add memory in the current environment limitlessly (they aren't making Windows servers that can hit the 64 bit max for memory) and SQL will use it natively.
Be warned, though, that 64 bit will make SSIS problematic at times. Many drivers that SSIS uses (most obviously the Jet ones, i.e. Excel and Access) only come in 32 bit forms and you have to go through a few hoops to use them (i.e. running SSIS in 32 bit mode).