UberCryxic, your claim that the treaty of Tilsit is completely accepted as the end of the 'Glory Years' is incorrect. In fact, i was of the opinion that the Glory years ended in December 1806 - And several major historians are in this camp. Just going from Chandler's authoritative work 'Campaigns of Napoleon', Chandler claims that Iena-Auerstadt was the height, and that December 1806 was the beginning of Napoleon's (and therefore La Grande Armée's) decline. He gives the following reasons for this.  
 * While the twin victories of Iena-Auerstadt were complete (with 70% of the Prussian army becoming either casualties or prisoners), Napoleon had failed in his efforts to bring a swift conclusion to the war. Königin Louise of Prussia had managed to persuade her husband not to sue for peace. This meant that the Tsar's army was now also drawn into the war, an eventuality which Napoleon did not desire. Instead of a 'blitzkreig' style campaign (as at Austerlitz), he was now forced into an unwanted winter campaign in Poland, and while his victory at Friedland was spectacular, It was merely the conclusion to an unwanted and costly campaign. 
 * The introduction of the Continental System with the [[Berlin Decree of November 1806 was to lead to the Invasion of Portugal in 1807 and of Spain in 1808, so therefore to the Peninsular War (The Spanish ulcer ruined me). This was also the reason for the disastrous Russian Campaign of 1812.  
 * Finally, from this point Napoleon was no longer seen as invicible. Although Imperial publicity painted Eylau as a great victory, the true nature of the battle was leaked out, and this dent in Napoleon's invincibility hardened the resolve of those fighting Napoleon to 'stay the course. Also, for the first time La Grande Armée was unhappy with it's commander (It was during the 1806-7 winter campaign that the Grenadiers a Pied received the nickname 'les grognards' for openly voicing their concerns to the Emperor.  
 In conclusion, to state that Friedland is the end of the Glory Years ignores the equally popular school of thought that December 1806 saw the end of this period.