S.H.
We had it done in April of last year. I thought it was a good time, between big heating and cooling parts of the year. The gas company had a deal, so I took them up on it. It was how I found out I needed a new heater. =/
Anyway. The air quality is MUCH better now, and my filter is hardly getting dusty at all.
The only problem is they left metal shavings in my laundry room (room attached to the heater area) and it was very difficult to get out of my Berber carpet, for weeks.
So I recommend it, just make sure they clean up when they are done, if they have to adjust any duct holes at all. =)