welcome back, Craig.
re: >>>just got interested in making my own version of www.yrwall.com
I can't speak to that whole application area. Not sure how great of a 'tool' OpusPro is for giving users creativity space at runtime. I would guess AJAX suites or Google apps are more likely the drivers behinds major developments... especially if in a collaborative space.
That said, I am very happy with Opus for development... and I am impressed with its fine graphics capabilities in terms of shapes and shading, resolution, etc.
If you download the latest OpusPro trial, and look at the Sample Publications shipped with it... you will see the rudimentory 'paint and place' coloring examples. There is also now script commands for giving users drawing capability... you decide.
cheers.