Are these kind of filters just utterly unappealing to anyone else? It would be like if your iPhone's accelerometer emulated a CD skipping when you went jogging. (startup/app idea?)
I find them quite appealing because the output from my mobile phone camera is usually so staggeringly bad that the filters are the only thing that can save them.
As cameras keep getting better, filters might decline in popularity.
Someone needs to make an SDK for photo filters that allow apps to easily put photo filters in their app. It seems like you would be able to charge for this pretty easily as well.
Apple already did this, back in 10.4, with Core Image. It will be added to iOS whenever iOS 5 is out.