Is there any specific sectors of Software Engineer/Computer Science where there's a marked difference when developing for 64 bit systems? I've been coding for around 10 years now, and since the break of 64 bit systems, my code hasn't changed one bit.
What applications that a single coder can code as a side project require you to use 64 bit technology?
Anything that requires more than 4 GB of working and program memory would certainly qualify, since that is the maximum amount of memory that a 32 bit system can address directly.
Since 64 bit numbers can reside in the CPU registers, calculations requiring numbers of these sizes would see a performance improvement.
We recently ported some of our internally-used libraries to 64-bit. The C code didn't change at all; we just had to get the 64-bit versions of the third-party libraries we link against and figure out which new compiler directives we needed to use. The biggest headache was finding 64-bit versions of our dependencies and refactoring our build system to handle both 32-bit and 64-bit.
That's not to say that other software wouldn't require modification. For example, if you pack your data to fit within word boundaries, you might now be inclined to pack it differently when programming for a 64-bit system.
Aside from address space or big calculations, doubling your word size helps more in the low level stuff, and mostly for people who are going to be doing kernel hacking or writing device drivers. For instance, let's say you have a stream of bytes from a network connection and you have to process them. You can now pull those bytes in from main memory to CPU registers 8 at a time rather than 4. But I would think you need a "64 bit aware" string library to take advantage of this.
Anecdotally, we did observe a performance increase when upgrading from 32 bit SQL Server to 64 bit SQL Server (2005) on the same hardware (a 64 bit machine).
If you need to ask, you probably will not get any advantage, as you are probably not building into your code any assumptions about size of ints. Rather few use cases, and all fairly low-level, will see any speedup. Bignums and heavy integer arithmetic on very large numbers will be quicker (like crypto).