Tell me about the plane. What are its gotchas? Good points?
Off the top of my head...
Good points: Very efficient - Diamond extracts more knots per gallon than any other non-complex airplane. On the "older" ones, you should see around 140KTAS on around 10 GPH. It hold 40 gallons standard, though there is a long-range option with 50 gallons. Still, 420nm with an hour reserve is pretty good, and it'll get you there quick enough that you might not have to make a beeline for the bathroom.
Visibility is amazing. You have about a 210-degree panorama horizontally, you can look pretty much straight up, and straight down even though it's a low wing because the high aspect ratio (read: narrow) wing's leading edge is about at the back of the pilot's seat. You can also (Well, I can) see down in front quite well (like 30 degrees below level) due to the sloped cowl. The visibility makes me feel more like *I* am flying, rather than just sitting in a little tin can up in the air.
Glide ratio is very good, so you have more options in the event of an engine failure. Safety record is very good as well, I think the only DA40 fatalities so far resulted from a botched instrument approach into power lines.
Bad points: It might be a bit hot on very sunny days. Newer models have more of the canopy painted on top, but honestly I like the older ones better in that regard. I like that visibility! Also, you can lock the canopy about 4" open on the ground on hot days, so it'll just be the few moments prior to takeoff that'll be really hot. You'll want to get a cover for when it's parked, though.
It's not made for really really tall people. If you're over 6'4", forget it. I put the rudder pedals all the way forward and I'm comfortable until I put my thickly-padded Lightspeeds on, and then I have to slouch just a bit to not bump my head on the canopy. If my club gets a DA40, I'm planning on getting an in-ear headset to give me more clearance.
The stall warning is freakin' annoying. It comes on WAY above the stall, so you'll hear it way too often, and you probably cannot land without it coming on. IMHO, this needs to be fixed so that people don't ignore it.
Since the wings are so narrow, the tanks are long and if you're not topped off or fairly close to it, you can't see fuel in the tanks. They include a fuel level measuring device that's pretty weird - It hooks to the sump drains and you put it on a notch in the leading edge of the wing. Fuel flows into it and you read the level. Not necessarily a bad thing, but it is odd.
General info: The vast majority of these (non-G1000) were equipped with 530+430, KAP 140 autopilot, slaved HSI, premium interior. Those that do not have this level of equipment will take a big hit on resale. Expect prices in the $175,000 range equipped like this, and much lower if not. Embry-Riddle had a bunch with no autopilot that have been for sale recently, and ASI Jet Center has one that had King avionics instead of Garmin (there is/was that option, but almost nobody took it) that has been for sale forever. (At least two years, and hasn't sold even when they cut the price way down. I think it's still out there with "make an offer" listed... N465DS.) Point: Try to find one with 530/430/autopilot installed already if you ever want to be able to sell it for much.
There is an owners group, DAPO, at dapo.org that has a forum that's pretty darn good.
The most common mechanical problem is cracked exhaust risers, so pay special attention to those on the pre-buy.
Most of the earlier ones had the 3-blade composite MT prop. Be nice to it, I don't think you can repair them as easily as the metal ones.
With the center stick mounted in the seat, you may not be able to give a ride to someone wearing a skirt!
However, it does give you a good view of the panel.
The engine gauges are in one big electronic display, the
Vision Microsystems VM1000.
I've found the best technique for flying it is to not actually touch the stick, but to hold your hand around the stick in a circle and then just kind of "think" it in the direction you want it to go. It takes just a very light touch. Nimble, but not unstable at all (which is why it flies so well when you're not holding on to the stick!) It maneuvers very nicely as well, and once you get the hang of flying it, it's an easy bird to land too. Or, maybe I've just gotten really lucky. I've never had a bad landing in one, and my best landing ever was in one - I'd never believed it was possible to not know you'd landed until it happened to me!
If you have a yoke board or yoke-mounted GPS, you might need to invest in some new hardware. Zuluworks makes a "Mini-Z" board that's designed with the DA40 in mind (Zuluworks' owner, Rob Honeycutt, owns a DA40).
Despite what Grant said and what you may think based on Cirrus' performance, the DA40 is actually an excellent short-field machine. I forget the exact numbers for each, but it compares favorably with a 182.
Useful load is best-in-class. 660 pounds or so. The older birds do have a slightly lower landing weight, but I believe you can do something to remove that restriction, the newer ones from the factory don't have that limitation. (A good question to ask of DAPO.)
Hope this helps!
Kent