I think that the DA40 is the best overall sub-200hp 4-seat certified single around. Easy to fly yet still nimble and sporty, astoundingly efficient, amazing visibility, and just all-around fun. They also have an excellent safety record. Not everyone likes them, and here's some of the quirks: (Remember, every plane has its quirks, you just pick the ones you want to live with!)
* Seats do not adjust - The rudder pedals do.
* Castering nosewheel
* Long wings - 39 ft 2 in wingspan makes it a little harder to get into a 40-ft hangar, so you may end up with more hangar rash if you're not careful
* Can't see the fuel in the tanks after you've burned off a fairly small amount. This is due to the long, high-aspect-ratio wings and dihedral. Diamond includes a nifty tube arrangement that you can use to accurately determine your fuel load during preflight, however, so this isn't that big of a deal.
* The stall warning horns on the ones I've flown tend to go off WAY before the stall (at least 10 knots). Thus, they'll sometimes chirp in moderate or greater turbulence, they'll chirp with a little less turbulence on final, and they'll pretty much blare on every landing. Dunno if they've fixed this yet or not. (This is the one thing that really annoys me about it.)
* It cruises well into the yellow arc, which starts at 129 KIAS. I was told by a Diamond rep that the yellow arc is a function of stall speed and since their stall speed is pretty low, the yellow arc starts fairly low too. He also said it's perfectly OK to fly it in the yellow arc all the time, even with some chop or turbulence.
I guess if you want to keep it in the green, you pull the power back a bit and save some fuel, or you just go higher.
* If you don't learn to steer on your takeoff and landing rolls using the rudder as soon as it's effective, you'll burn up your brakes in a hurry.
* Slippery airframe, so speed control on final approach is essential to making good landings and not floating forever.
Really, like many other planes, if you fly it like it's a Cessna or Cherokee, you'll probably be disappointed and maybe break something. Learn how to fly it right (which is not difficult at all), and you'll find it's quite a sweet bird.
As far as safety, last I checked there had only been a single fatal accident in the type, and that was when a pilot flew it into power lines on approach. They tend to NOT burn after crashes which greatly increases survivability. They're also the only composite certified airplane that I know of that does not have an airframe life limit. On a Cirrus, for example, after 12,000 hours you own an expensive piece of artwork. They did this by doing load testing on a wing with one main spar - The airplane actually has dual main wing spars. Since it passed the tests with only one spar, the FAA certified it for unlimited airframe life.
Hope this helps!