Yes, this is a great little engine. It's simple, quiet, easy to maintain, and everything is easy to get to (well, depending on your boat too I guess).
The impeller incident Henry writes about is not uncommon. Same thing happened on my dad's old Columbia 31. One fin of the impeller wedged itself in the cooling system and essentially stopped all water flow. It didn't sieze, but it did require a major overhaul. I remember as a kid having one winter with A4 parts spread all over the basement :-).
3 key things w/ A4 impellors:
1) Always carry at least one spare and know how to change it at sea. If you want to make it easy on yourself, get one of those aftermarket kits with the thumbscrews and the quick release cover.
2) Change it every spring religiously. Doesn't matter how much you used the boat last year, just change it. If you didn't use it much, keep the old one as a spare, but mark it with a tag as limited lifespan spare only.
3) Install a simple temp and oil pressure alarm. I found one at Boat US for under $20. Very easy to wire and install. Put the buzzer where you can hear it from the helm, and maybe wire a light to it as well. That way if the engine does begin to overheat, you'll know hopefully before any damage is done.
Othewise this is a great engine. I've got mine running so well that it'll idle at about 100 RPM IN GEAR!
This is always a good resource if you have questions or problems with your A4.