Yeah I would avoid the horizontal scrolling site, especially making one that loads more content as you scroll.
The main reason is that it is hard to scroll, unless you make the mouse wheel work with horizontal scrolling (which is possible) and the second reason is because of the Opera width bug. The width of web pages is limited to 32766, and it still exists! – try this demo in Opera… if you go to past slide 35, all you’ll see is a blank window because the images have wrapped around to the next line.
Edit: LMAO just as I finished this post, I accidentally closed Opera and reopened it. It updated to version 11.60 build 1185 and the slider started working past slide 35… FINALLY!