As a harp player, I can definitely concur with the verdict of (I think it was) Igor Stravinsky, who said, "Harpists spend 90% of their lives tuning their harps and the other 10% playing out of tune."
Keeping a harp in tune can be tricky. For one thing, there are a whole lot of strings on a harp. The most strings you get on a guitar is 12; the fewest strings I've seen on the smallest Celtic harps is 22. My Dusty has 36; full-sized orchestral harps often have 47. That's a lot of strings to keep in tune.
(Incidentally, to get a sense of what my big harp looks like, go to this page and look at the bottom pictures, of harps made of bubinga.)
For another thing, all but the smallest harps use multiple types of strings. My Dusty has many nylon monofilament strings; it has several strings with nylon monofilament cores with nylon wrappings to add mass (giving them rougher textures); and six strings or so with bronze cores and nylon wraps. All these strings react to changes in temperatures differently. If a cold breeze hits the harp, the metal-core strings all try to contract, and the tension goes up, causing them to go sharp; this doesn't immediately happen to the nylon strings. But eventually the wood starts to cool off and contract slightly, causing all the strings to relax a little and go flat. The net effect is for the the bass strings to go sharp and the others to go flat, and this can happen rather quickly and unpredictably.
Many harps--including the higher-end ones--use a couple octaves' worth gut strings in the middle-range. Gut tends to continue stretching throughout the life of the string; it must be tuned a little tighter every time you play it, until the strings eventually break. The gut strings also tend to be very sensitive to moisture in the air.
One other factor that makes harps hard to tune--at least, it did before the creation of electronic tuners--is that vibrations in one string cause other strings with compatible harmonics to start vibrating automatically. And the strings don't have to be perfectly in tune for this to happen; plucking one string causes many others to start sounding, so long as it's within a few cycles per second of the optimal tuning. This makes it difficult to tell whether you have it in pitch or not. One string may be a few cycles per second flat, but it will cause the previously-tuned strings to play, obscuring the fact that you're still a little out of tune. Thankfully, this problem was mostly solved when electronic tuners came in. (Although, for those with over-evolved tastes in music, this causes new problems, since the electronic tuners give you a tempered tuning, and tuning by ear gives you a system based on perfect fifths, which sounds just a wee bit different. As I said, though, modern audiences have to be over-evolved to notice this. Bach would probably cringe, though.)
Anyway, it was with great interest that I saw this:
It would seem that Gibson has come out with a model called the "Robot Guitar" that has a built-in tuning mechanism. From the moment it recieves the command, it can tune itself in a couple of seconds. They apparently incorporate an electronic tuner into the guitar, and use it to drive little servo motors attached to the tuning pins.
The guitar runs for about $2500.
So naturally, I started thinking about what it would take to put this sort of thing on a harp.
I think the answer is: a heckuva lot more than $2500. Every single one of those tuning pins--36 on my dusty, 47 on a full-sized Concert Pedal Grand Harp--would need a servo motor and some mechanism to sound the string. And (especially on the harps that don't have pedals) you'd need some way of specifying which tuning scheme you want to use. I use E-flat, but some people use C or something more exotic, especially when doing non-traditional music. And of course, there are plenty of over-evolved snobs who don't want their harps done with (sniff...) tempered tuning.
Furthermore, installation of these servo motors would weaken the arch. All those tuning pins have a way of acting as a row of splitting wedges on the arch of any normal harp; splits in the arches are a fairly common harp repair as it is. Removing even more material from the arch to accomodate the motors would weaken it further.
Add that to the fact that my Dusty would cost $5145.00 to buy it new, without any newfangled, high-falutin tuning mechanism.
So, maybe it's not too practical. Ah, but one can dream...