The three Google products I use most frequently - Gmail, Search, Maps - have been underperforming heavily lately. Search is useless unless you really tailor your query to find organic results (throwing in "reddit.com" is almost a necessity). Gmail frequently lets harmful spam slip through, sometimes even tagging it with an 'important' label.

The decline in Maps has been the most visible, mostly because it has negatively impacted my commute at times. Google Maps will frequently reroute me through slow, complex side roads and will often completely miss main roads. On routes that I already know, I've stopped following Google's directions altogether because its hilariously off-target.