Place the flour in a resealable plastic bag. Add the beef to the bag, several pieces at a time, and shake to coat completely.
Heat a large saute pan over medium-high heat and add the oil. In batches if necessary, add the beef and cook, turning, for 8 to 10 minutes, until browned on all sides. Using tongs, transfer to paper towels to drain.
Place the beef, potatoes, carrots, onions, and thyme in the slow cooker and pour the beer over the top. If you prefer the vegetables to have more texture, let the stew cook for one hour before adding the vegetables. Cover and cook on low for 8 hours, or until the meat is very tender. Season with salt. Remove and discard the thyme sprigs.
Transfer to a serving bowl and garnish generously with parsley.
To make LAMB AND GUINESS STEW, use 4 to 6 lamb shanks and trim off as much fat as possible. The shanks will still render plenty of fat during cooking. For a lower-fat dish, cook them in the beer with 1/2 onion all day, then refrigerate overnight and remove the congealed fat before finishing the dish. Add the potatoes, carrots, onions, and thyme. Cover and cook on low for 2 to 3 hours before serving.