Indeed quite slow... However, I remember that in the past I've hit an issue that some GLES code was much much slower due to some messup with window compositing... I cannot give you any direct links now, I'm sorry Closest that I found is this post by javispedro: http://talk.maemo.org/showpost.php?p=576020&postcount=7 which seems to also mention clutter, gles, images, etc (maybe that's also the cause of need for backgronds in pvr format? maybe the gles renderer in clutter changes them internally to pvr format as our gpu may only support that, while the gl renderer doesn't do anything to textures as desktop gpus generally tend to support more formats etc?). I think javispedro could help you a lot with getting to know the whole graphics system, I consider him a guru of this stuff in Fremantle.

edit: qwazix in this thread http://talk.maemo.org/showthread.php?t=84987 also had some fights with clutter and other libs, maybe you could ask him about his advices and what he found during reviews of code.