Though a number of web-based CAT tools have emerged over recent years, to date the most common form of CAT tool used by translators remains the desktop-based CAT tool. However, currently none of the most commonly used desktop-based CAT tools provide a means of measuring translation speed at a segment level. This metric is important, as previous work on MT productivity testing has shown that edit distance can be a misleading measure of MT post-editing effort. In this paper we present iOmegaT, an instrumented version of a popular desktop-based open-source CAT tool called OmegaT. We survey a number of similar applications and outline some of the weaknesses of web-based CAT tools for experi- enced professional translators. On the basis of a two productivity test carried out using iOmegaT we show why it is important to be able to identify fast good post-editors to maximize MT utility and how this is problematic using only edit-distance measures. Finally, we argue how and why instrumentation could be added to more commonly used desktop-based CAT tools that are paid for by freelance translators if their privacy is respected.