Stomach ulcers, bleeding, potential colitis, liver damage and kidney failure with long term abuse. If the person who took it isn't having stomach pain or cramping, and isn't passing blood in their stool or vomit; if they are asymptomatic for a few days, they are likely fine.
Taken from wiki:
Ibuprofen overdose has become common since it was licensed for over the counter use. Many overdose experiences are reported in the medical literature, although the frequency of life-threatening complications from ibuprofen overdose is low. Human response in cases of overdose ranges from absence of symptoms to fatal outcome in spite of intensive care treatment. Most symptoms are an excess of the pharmacological action of ibuprofen and include abdominal pain, nausea, vomiting, drowsiness, dizziness, headache, tinnitus, and nystagmus. Rarely, more severe symptoms, such as gastrointestinal bleeding, seizures, metabolic acidosis, hyperkalaemia, hypotension, bradycardia, tachycardia, atrial fibrillation, coma, hepatic dysfunction, acute renal failure, cyanosis, respiratory depression, and cardiac arrest have been reported. The severity of symptoms varies with the ingested dose and the time elapsed; however, individual sensitivity also plays an important role. Generally, the symptoms observed with an overdose of ibuprofen are similar to the symptoms caused by overdoses of other NSAIDs.
Correlation between severity of symptoms and measured ibuprofen plasma levels is weak. Toxic effects are unlikely at doses below 100 mg/kg, but can be severe above 400 mg/kg (around 150 tablets of 200 mg units for an average man); however, large doses do not indicate the clinical course is likely to be lethal. It is not possible to determine a precise lethal dose, as this may vary with age, weight, and concomitant diseases of the individual patient.
Suffice to say, taking too much is not a good idea. Toxicity is variable to the point of unpredictability, and long term abuse will most certainly cause serious health problems.