While Core Image on iOS 5.0 lacks blur filters, there is still a way to get GPU-accelerated blurs of images and video. My open source GPUImage framework has multiple blur types, including Gaussian (using the GPUImageGaussianBlurFilter for a general Gaussian or the GPUImageFastBlurFilter for a hardware-optimized 9-hit Gaussian), box (using a GPUImageBoxBlurFilter), median (using a GPUImageMedianFilter), and a bilateral blur (using a GPUImageBilateralBlurFilter).
I describe the shaders used to pull off the hardware-optimized Gaussian blur in this answer, and you can examine the code I use for the rest within the framework. These filters run tens of times faster than any CPU-bound routine I’ve tried yet.
I’ve also incorporated these blurs into multi-stage processing effects, like unsharp masking, tilt-shift filtering, Canny edge detection, and Harris corner detection, all of which are available as filters within this framework.