My hotspot (9.0 and 9.1 betas) has worked fine with no issues - apart from occasionally getting a "failed to start hotspot" message as the connected icon appears as it connects just fine.
But I do have a general issue with this hotspot feature in that it doesn't connect automatically if not in range of a wifi network. Would it really be so difficult to set it up so that if no wifi is found it just pops up "Connect to Hotspot: Grumpy's iPhone? Yes/No"? Having to open settings, go to wifi, wait for the hotspot to appear, then tap it each and every time I want to tether to my phone annoys me no end. Especially since known wifi networks are just joined with no questions asked. Putting the popup up would just be a one step yes/no for anyone wanting to connect or not.