This is going to be a bummer, but it turns out that we jumped the gun yesterday when we reported that Tango would support fast app switching between 8 apps. As it turns out this feature was actually a clever new tweak thrown in by the creator of the HD2O custom ROM, HD2Owner. According to a recent post in a thread on XDA:
more tasks in taskswitcher is not a tango feature
it's just another useful tweak i implemented into my rom
That is a real shame as we know many would love to see this feature make it to all devices, not just the hacker-friendly ones. Looking at the bright side though, HD2Owner did managed to enable this on their own and the original story was picked up by the major news outlets so maybe Microsoft will consider enabling this in the final update. As far as we know though, Tango can still only multitask between 5 apps, NOT 8. (Sorry for the confusion!)
Big thanks to reader Keith V. Smith for letting us know about this!
Source: XDA-Developers Forum (HD2Owner)