Cokin filters

Does anyone have experience in using the Cokin range of gel filters?

Cokin webpage

I'm paticularly interested in graduated colour filters.

I have a Canon 20 D, Canon 10-22 mm lens, Ikelite housing and Ikelite 8 inch dome port.

Does anyone know whether a Cokin P series filter holder will fit inside this port?

Please ignore the second question. None of the Cokin holders is wide enough for this wide-angle lens. Only the screw-in 77 mm filters can be used.

I'd still like to know if anyone uses Cokin graduated colour filters