Bad Pen...
bestfriend,
The situation you descibed, where the dealer burns a card each round, can really kill the effective penetration. Furthermore, the problem is exacerbated as the number of players decreases, so the worst case is when you're playing one hand head's up against the dealer.
For example, assume after the shuffle that the dealer cuts off only one deck. At first, you're thinking, "Wow! 7/8 is 87.5% penetration! This is a candy store!" Now if you're playing one hand head's up against the dealer, then on average you and the dealer will each use 2.7 cards, for a total of 5.4. However, since the dealer also burns a card each round, in fact you'll be using on average 6.4 cards per round. Thus, the effective penetration will be 87.5%*(5.4/6.4) = 73.8% (assuming my slide rule didn't slip!), rather than the 87.5% you thought you were getting. Your candy store has given your wallet a cavity!
One way to ameliorate this situation is for you to play as many hands as possible. In the above example, if you play 7 spots against the dealer, then on average 2.7*(7+1) = 21.6 will be used, plus the extra burn card. Thus, the effective penetration will be 87.5%*(21.6/22.6) = 83.6%, which is like getting 6.7/8 penetration without the extra burn card.
Hope this helps!
Dog Hand