I too haven't any major issues with iOS8 performance or interaction-wise (iPhone 5 & iPad 3). Yes - seems apps launched the first time after upgrading are taking longer to load (and one App even lost it's security activation key - asking me to reactivate my device with their website). Seems the upgrade is "big" and possibly many deleted their cached data. Performance seems to be fine for second+ launches and I'm slowly discovering the new features hidden around the system.
Most annoying thing so far - "this app is tracking your location in the background" - seems Apple is going to ask me this question for each of my 100 apps that use location. More annoying - there is no option for "Only when app is Running" - either On or Off... unless the app supports that new mode. I don't want the weather app tracking my every move in the background - I'm willing to wait for them to update my current weather location when I open the app.
And biggest bug found so far - handsfree integration with my car stereo seems to be broken. Playlists selected won't play (although the car shows the time counting up) - fast forwarding through songs causes samples of audio to play, but silence otherwise, and sometimes loops on the first 1 second (inconsistent repeatability of the problem). Forcing it to fast-forward for about 30 seconds finally made it play. Or picking a playlist from the iPhone works fine (which requires hands-on).
Smallest bug - Unlock screen was overlaid on top of "now-playing" Album art making it impossible to see the PIN keys. After unlocking it I haven't seen this happen since (took a screen shot to prove it happened).
For a major OS upgrade - it seems to be working fine. Battery life seems to be the same, all apps are working, and nothing crashing.