There's been a great deal of focus on the 1999-2002 years of Mitt's Schrödinger's Cat-like status at Bain Capital and the related information on his tax returns from those years. But looking at the line in the sand he and his campaign have drawn to just releasing 2010 and estimates for 2011, I would propose that perhaps any troubling information in his tax returns is likely far more recent, say perhaps covering the years as recently as 2008 and 2009.
If you think about it, those are the years that would fall outside of the window of those Romney turned over to the McCain campaign for VP vetting back in early 2008 since those wouldn't be filed until long after Sarah Palin had been selected as the GOP's VP nominee. Frankly, outside of the discrepancies regarding his involvement in Bain Capital, I'd be far more interested to see where his income came from during 2008 and 2009 while the housing market and the economy was busy melting down. I think the reason they don't want to release any returns from before 2010 is because he directly benefitted in a big way as a result of the economic and housing market downturn. Even Mitt Romney must realize that the optics of him laughing all the way to the bank while millions of Americans lost so much during those years could be enough to tank his campaign for good.
And who knows, perhaps it could possibly sink him before he officially secures the nomination from his party at the RNC convention? Can anyone say "brokered convention", my friends? The circus may not be over yet!