Hmm, page load times are a tricky thing...
I am on a crappy ADSL (phone based) internet connection (2760 kbps down, 860 kbps up). If I max out my upload speed, my download speed tanks. That would cause your site to load slowly for me.
There's also images. If you have a banner for a fluid skin, and you make it a 2560x120 (width x height) image and use CSS trickery to shrink it for smaller screens, that's still a gigantic image and the banner should be redesigned to feature a gradient for the "middle" component. In other words, have a "start" and "end" image at, say, 200x120 and use CSS gradients to fill out the "middle" bit (gradients are small 1x120 - to follow the size examples I've used thus far - images that are just repeated as needed, and are thus pretty small).
Next up is JavaScript, the more JS files you have hosted locally as opposed to remotely, the longer page load times are.
Unless your MySQL server is slow as an old dog, it's quite likely that the SQL server is not the bottleneck when you're looking at how to speed up your site.
vB Optimise focuses mainly on improving the MySQL aspect. That being said, v3.0.0 (which is currently in an opt-in beta) does support CDN (Content Delivery Network) which, depending on your provider, will speed up the images and JS aspects by quite a bit.
For reasons I do not understand, browsers can only download 1 image at a time from a local server, whereas remote content can be downloaded synchronously. That's why it's recommended to let a 3rd party like Google host jQuery (via the vBulletin options) as opposed to serving jQuery locally.
For people with a single-server setup (i.e. web server and database server on the same server) it's quite possible that vB Optimise, even the stable v2.3.0, could improve page loads due to the fact that the less time your server has to spend asking and waiting for MySQL to query and answer (as opposed to simply asking a RAM-based cache system like APC for the query result), the more time it can spend on pushing more internets through the tubes to your browser
I had a quick look on your front page, and it loaded pretty damn quick for me (I don't have YSlow data or anything so it's all "feel"
) - I think the only thing that might slow your page loads down would be all those social media and network integration buttons - for each of those, they have to check if you're logged in to the site in question and fetch the "like" count or whatever.
But I don't actually know how those things work (though I am convinced they use some combination of black magic and magnets) so I may be wrong in saying that they slow down the page.
Hope this wasn't too fragmented and without structure, I pretty much just wrote it in one go as I thought of things to say. I am exceptionally horrible at explaining things to people, so have no worry about asking me to stop rambling and start making sense
