I read a fair number of novels set in and around this time period and it's not unusual for any given character to refer to the 'war' or for a hero to be scarred by his experiences on the Peninsula. Even if you don't read any of the accounts written by eyewitnesses of the time the cold, hard statistics are enough to provide a rough (and horrific) idea of what it may have been like.
According to the British Battles website:
The British, Belgians, Dutch and Germans lost 15,000 casualties or 1 in 4 engaged. The Prussians lost 7,000. The casualties of the French army are estimated at 25,000 dead and wounded, 8,000 prisoners and 220 guns lost.
This may not seem many in light of modern warfare's capability for destruction, but for one day's fighting when your main weapons are cannon, rifles and swords (and horses!) it's quite a sobering achievement.