Ian -
If the objective of the 'default' (non-fluid) setting is to improve the look for mobile devices, any chance that we could have a test for mobile browser type, set that to the non-fluid mode, and let all of the desktop folks have the fluid mode by default? As it stands now, if I'm following this, all existing and new users are going to be seeing the 'non-fluid' version unless/until they notice this thread or somehow otherwise discover the option.
Unfortunately, we'll need to use the fixed width version as a default - as the reasons are more complex than they may appear. Both the fluid and fixed style should actually look the same on a mobile device, as they'll collapse in the same way as the screen shrinks. However, the changes from the old layout are much more evident on the mobile style (reduced clutter, improved registration/login buttons, etc...).
Most of the forum plugins and style elements we use are assuming a fixed width site, so updating them is very time consuming work with our old custom style. The new style is actually really close to the stock design, but using overriding CSS instead of customisation to the CSS, meaning we can roll out changes much quicker - plus I can be certain what they'll look like on a users monitor. I'm happy to have the fluid style as an option for those that ask for it, but it's not the supported or default one - I suspect it'll work fine for logged in users, as a lot of the problematic areas will be guest customisations we've made.
FWIW, a lot of forum software is moving in the direction of fixed styles, as monitors are getting so large it's hard to get designs that work well on all screen sizes. Here's a demo of the new version of XF2.0 (we won't be upgrading to this until it's been stable for a while):
https://xf2demo.xenforo.com/
I can completely understand why you guys would prefer fluid versions, so I'm happy to have it as an option (I also prefer it on some sites myself). However, having it as the default supported type would involve increasing amounts of work moving forward, so I'd rather have it as something I can patch as soon as bugs/updates are available without the risk of breaking anything.