a. faster loading of pages since the main forum content will load first before the slower loading sidebar scripts (rss feeds, skycraper ad, which can be flash and slow-loading, gallery thumbs, etc).
b. the sidebar boxes will be nearer the cursor (easier access) which is usually on the right side (near the scrollbar)
c. for smaller monitors, the main forum content will still be visible. what will be cut-off are the sidebar content.
d. isn't it nice to have change once in a while, provided that the change does bring some benefits...
If I may say so, I think the sidebar is better suited for the space above the forum, above the shoutbox. That space takes up a lot of vertical room which I'm sure Tsikoteers will have to bypass to get to the main forum section. The Google ads there actually take up 1/2 the space of my monitor when fully scrolled up.
That Smirnoff advertisement is also a bit large, IMO.