I've created two new styles for the forums derived from the vBulletin 3.5 stock templates. Although they look somewhat similar to the 3.0 templates, there are quite a number of differences under the hood that break things in subtle ways. The most obvious of these was the missing "quick post" feature.
The two new styles are named MP3Car vBulletin 3.5 Standard and MP3Car vBulletin 3.5 2-Column The "standard" version is closer to the default style newly adopted in vBulletin 3.5. The "2-column" version looks much like the template you were used to seeing before the upgrades. I've set the default to the new "2-column" format, so if you don't have a style selected in your profile (and I believe nobody does by default) you should now be seeing the new 2-column format. (If not, log out of the forums and log back in again.) I've kept the old vBulletin 3.0.x style arround just in case I goofed something else, so y'all can switch back to that instead of yelling. ;-)
There is also a quick style switcher at the bottom left of every page, so you can flip between the formats to see which one you like best. HOWEVER, if you switch to the old 3.0.x style, this quick switcher will *not* work -- you will need to go into your options panel to select one of the 3.5-based styles.
I'll be keeping the old 3.0.x style arround for a few days "just in case" and the plan is for that style to go away. If there is something broken with the new 3.5 styles, please let me know and I'll take care of it.
Please note: Quick Post still DOES NOT WORK with the old 3.0.x template. Anyone who complains about this will have their post count reset to zero. ;-)