I love Hummingbird and it makes my sites super fast. I even wrote a theme that takes advantage of HB features especially moving assets to the footer. The only problem I have had recently is that every time I update plugins, the sites break and HB's cached asset files go missing or are incompatible with the updates, so I have to go through and clear the caches and move all the files again and things are back to great. If I had one site, or maybe 20 sites, that would just be something I would put up with, but I have hundreds of sites across several MultiSite installs, and I can't go through every site and clear the cache. I would like to see some sort of global HB asset cache flush so I can just update plugins, then flush the caches in one or 2 steps.