My situation is that my wife and I are retired and currently in a lower tax bracket than we will be in when I start drawing SS.  It seems to me, then, that it would be a good idea to do partial Roth conversions from my IRA each year until I file.  Are there any "gotchas" I need to be concerned about with respect/ to this plan?  In terms of taxes, just have the taxes withheld as I do conversions, or... ?

The alternative would be to begin taking SS next year at 62 and just wait for required disbursements.  The numbers I ran suggest that delaying SS until 66 and doing Roth conversions now would allow me to "catch up" on the early application SS payments (at age 62) by age 70 rather than the normal age 78.  Seems like a decent strategy...

It's a good strategy. Gotcha's are obvious and I'm sure you already considered them. You only want to convert up to whatever amount keeps you in the 15% Federal Tax bracket; if you and your wife die before average life expectancy than delaying SS may not be best otherwise it is worthwhile.

You can withhold taxes as you go. 

I have a slightly different take on this. I believe that the question of whether or not to convert should be principaly based on one thing: have you or have you not reached your financial target (ie. the amount you think you'll need last for the rest of your retirement)?

If you haven't reached the goal yet, then it's in your interest to keep the leverage of what you would otherwise lose in taxes so you reach your goal sooner.

If you've already reached your goal, then convert as aggressively as you can (without of course dropping below the goal amount due to taxes).