I just had my garage door re-done, so I had the Sears opener installed (53965). So far, so good.
The installer happened to be a friend, and despite him being a Genie dealer, advised me to go purchase the Sears unit for him to install (said that they were much more reliable).
He took about $100 to install, and it took those two guys about an hour to knock it out. Considering I've never done one, I'd say it would take me about 3 hours or so to get it done. Also factoring in the fact that I wouldn't want my garage door crashing down on anyone (or God forbid, the car!!) - I passed on doing it myself.
It all comes down to time and money - I think Sears will provide installation for $125, and they guarantee the installation. If a few hours putzing around with the opener doesn't bother you, then go for it. If you value you spare time (and would rather be waxing your car) then let these guys come and take care of it for you.