I just posted a new project on my software page. It's a fixed effects panel analysis function. It uses a method from econometrics to detect trends over time across a window of pixels. This increases the robustness of trend analysis as compared to a pixel by pixel regression analysis. An added benefit is the speed you gain as you downscale the original data by a factor defined by the panel size used. The function makes use of the Panel Data Econometrics "plm" package in R. A detailed overview can be found in this publication.
For a project in the Alaska I ran a quick analysis on MODIS GPP trends across the whole dataset (2001-2013). Below you see the results of a panel analyis of the MODIS GPP data using a panel size of 11 or roughly ~1/10 a degree. Given the pronounced warming of the Arctic a steady increase in GPP is noted across Alaska (up to 0.03 Kg C m -2).