Support for the notion that PC gaming is dying: Civilization V, Spore, Supreme Commander 2, Dragon Age 2 (maybe). All dumbed-down versions of their predecessors. The current selection of PC games at retail stores. The trend of UI for PC games. Mandatory online DRM for single player games. Lack of innovation in the past decade/consolidation of genres. Games run like shit even on modern PCs. "Ship now, patch later". Shift towards netbooks/phones/tablets.
Support against the notion that PC gaming is dying: Steam holiday sales (AAA titles for poverty prices), wide-berth of indie games, probably more AAA titles released per year now more than ever, digital downloads, nearly the entire back catalog of PC games available to play (GOG) on modern hardware. Integrated graphics are good enough to play games from several years ago on minimal settings.
Regardless of where you stand on the issue, one thing is for certain: PC gaming is definitely not like it used to be.