One of life’s small problems – I have imported some 500 RAW photos to my iPad from my dSLR (using Camera Connection Kit), but this takes loads of space on the iPad. You can delete photos using the Photos app on the iPad, but it is very slow for larger number of photos.
The solution? Open “Image Capture” on OS X, simple mark all photos and press delete. Be careful though, it will be able to delete everything from the Camera Roll, so especially if you have an iPad 2 (with built in camera), be careful not to delete those photos.
A small performance tip – do not have the iPad Photos app open at the same time you do this, it will slow things down a lot or even crash the iPad.