You will want to get a sense of general seasonality for your most important keywords or top queries.

First you will want to get a sense of seasonal volatility by running your top queries through Google Trends :

Pay attention to the average index of interest over time, since it can be a bit confusing; 100 here represents the highest search volume there has ever been, it is not the integer for number of searches.

So what you are looking for is that the current interest has not fallen off completely, looking at the graph it seems the current search volume for keyword research is down about 50% from what it was in August 2010.