Yes, I have a UPS/power conditioner (APC J15) and I believe that they are useful since I have a DLP TV & a DirecTV DVR. The UPS helps protect the TV's projection bulb from unexpected quick shutdowns, and the UPS also keeps the DVR from resetting everytime there is a power surge.
I live in the north Houston area and even though one would expect our power to be clean and reliable, it is not. Power surges and brief outages are frequent enought that I would not want to be without an UPS.
As you may have noticed, I have not mentioned the power conditioning capabilites of the APC J15 yet. When I bought this unit three years ago I was mainly interested in buying a UPS large enough to handle the load of my entire HT system. Non-commerical grade UPS's of this size almost always include a power conditioner (commerical grade UPSs do not). Anyway, the front display of the J15 has indicator lights, and a full display, that tells you when either the UPS or the power conditioners are active. Over the past three years I have been very surprised by how many times I have noticed that the power conditioner is active, or that the UPS has kicked-in even though there was not an obivous surge or brief outage. No one can tell for sure that a power conditioner is needed; most will say they are not. I am on the fence, but with all the times that I have noticed that the conditioners have been active I have to believe that; 1) the AC power is not clean or reliable, and 2) a conditioner can only help such situations.
As for you projector, I would not recommend a long extension cord connection. Just bad electrical policy IMO. However, a UPS or power conditioner may still be worth the costs depending what other equipment you have in your main equipment rack (a DVR would be my main red flag).
