I rather suspect that there's some volatility involved in all this. For starters, conference boosts tend to evaporate very quickly indeed – and while that may not explain why Labour's rise has solidified somewhat, it probably accounts for the Tory half of the equation. As for Labour's boost, you can only speculate. The learned Anthony Wells thinks it may be due to Gordon Brown's response to the Legg letters, but a hundred different people seem to have a hundred different theories. Besides, the position is far from terrible for the Tories: they're still around 10 points ahead, and they're consistently hitting 40 percent plus again, after a short spell in the 30s during September.
Overall, though, I wouldn't read too much into it all. Far better to wait until Parliament has been sitting for a while longer, and politics – as well as the polls – has been given a chance to settle.