I started it for when my heroic tier campaign was going on a cross-country trip to deliver undeniable proof of demonic incursions in their home village to the Emperor. Originally I had used that template to assign monsters to each card and deal them for each encounter. Mechanically I wanted them to gain a level during the trip, and with 52 cards, that gives you 10 encounters w/ 5 monsters each, with 3 extra for variety, so about one level. I took the levels from the suggested encounters from the DMG, tuning it a little harder as my crew was running 6 players at the time with some stupid synergy (Human Fighter, Half-Elf Warlord, Eladrin Rogue, Eladrin Wizard, Tiefling Feylock, and Human Archer Ranger)
About halfway through the trip, I decided that the leveling curve was slower than I'd like, so instead of adhocing levels, I granted bonus xp for each milestone beyond the first, so I abandoned the assigning cards for each level, and just left it tuned hard to keep them from hitting Milestone 4. Milestone 2, 3, and 4 would give each player the exp of an equal level monster, elite, and solo respectively. You'd be amazed how the Solo Exp Carrot can influence decisions on when to rest.
If you want to balance it down closer to party level, you are going to want to change enough of the pluses to minuses to take the total down by about 25-30 (if I mathed it right).
