It's important that you make sure all of the software you need to run your organization is available in a 64-bit version so you can continue to use it.
For nonprofits that manage many computers, an IT department might have trouble acquiring and supporting new operating systems, drivers, and applications. It's expensive enough buying the faster hardware, but getting a second set of software licenses for 64-bit operating systems and applications might be beyond the means of an organization with a limited budget. Furthermore, nonprofits, charities, and libraries often have to deal with erratic IT budgets and donated computers, which means they're more likely to wind up with a mix of 32-bit and 64-bit machines.
In these circumstances, some organizations opt to transition gradually, upgrading hardware first, then operating systems, then applications. Other organizations focus entirely on their servers and leave their desktop machines alone. Servers typically run the most resource-intensive applications, so they see greater benefits from upgrading to a 64-bit platform.