Getty Images; Alyssa Powell/BIYou know that shaky, nauseated feeling you get when you've had too much coffee? That's how Starbucks itself is feeling these days. At peak hours, its ubiquitous cafés are overcrowded and slow. Garbled names written in Sharpie have been replaced by computer-printed stickers for online-ordering overachievers, who are allowed to jump the line.