I know Zogby doesn't walk on water the way some say, and I know that Battleground is about as good a group as you can get. I don't think that either should be ignored; it is better to look at polls as pictures taken from slightly different angles.
By their very nature, polls are not precise. When you think about it, the large sample polls have margins of error of +/-3 points per candidate, and most polls have margins of error slightly higher. This means that two polls, done with the same methods even, could differ by 6 or more points without there being any reason other than random chance (and actually, by random chance, 1 in 20 would differ by even more than that, without anything being "wrong" per se).
I find that Zogby's state polls and his demographic breakdowns on his final poll during the 2000 election undercut the assertion that he nailed the election, though.