Evaluation of any efforts undertaken by a non-profit organization is becoming increasingly important. It is important to be able to evaluate the effectiveness of the expenditures of money and other organizational resources because there is usually not enough of either. In making choices, the organization always wants to maximize the results that it can obtain, and it is not possible to do this without some metric by which to evaluate the success of an expenditure of resources. The most effective evaluations are not exercises that are tacked on as an afterthought, when the expenditure has been completed, but instead is accomplished most effectively when it is built into the endeavor at the outset. Capacity building is no different from the other activities of your organization. You should build an evaluation procedure into your capacity assessment and subsequent capacity building activities so, when the process has proceeded, you will be able to discern the degree to which you have been effective.
Resources
If you want to understand exactly what evaluation is and why it can change the way in which you do things, this article from Creating the Future is a very good overview.
A set of links to resources on community needs assessment, data collection and analysis, evaluation process, logic model, organizational evaluation, outcome evaluation and program evaluation. (Nonprofit and Philanthropy Good Practice, Johnson Center at Grand Valley State University)
Another set of annotated links on a broad array of topics related to evaluation. (Foundation Center)