So, it actually did take all day yesterday.
Thankfully this upgrade has been a lot smoother than any I can remember before it. Marcel was beat yesterday and went to bed at 1am, he started at 10.30am yesterday morning.
I can't stress enough how many hacks and hooks we have in IPB (since the v1.0 days) that still aren't included with vanilla IPB and due to our server setup (syncing between databases and Apache servers etc) adding any modifications is quite a bit of work. Even the simple ones like show post stars when there is a member badge is a Neowin hack, so we're talking about a few handfuls of modifications here.
Basically DaveLegg took over last night and ensured that the site could come back online without all of our hacks, those will be added today.
Timan has also been working through the night tweaking the skin.
It could be worse, and as far as everything goes I'm happy with the result.
Please report issues to Site and Forum Issues but we're most likely already aware of them. I'll update this post when we're done, after that we'll be very interested to see if stuff is still broke.