Glad to.
For starters most other manufacturers offer pro and enthusiast models with higher max sync speeds than any current Pentax DSLR. If you're unfamiliar with the advantages of a higher max sync speed, it allows you to balance flash with daylight more easily. My PZ-1p has a max sync of 1/250, so Pentax knows how to do it, but it's as if they figured 1/180th should be good enough for everyone. There are of course people who will downplay it's importance, but they're obviously not trying to shoot the things I'm shooting.
Next, the Canon system does this really neat trick, they have separated camera EV compensation from flash EV compensation. Camera EV comp controls the ambient light, and flash EV comp controls the flash exposure. It's so intuitive. With Pentax (and Nikon) the camera's EV comp affects the flash exposure as well. So if you have a properly exposed flash picture, but you want to darken the background a bit to emphasize your subject, on a Canon, you would just dial in -1 EV on the camera, and the background will get darker, but the subject (lit by the flash) will stay the same. On a Pentax in the same situation, if you dial in -1 EV on the camera, you will not have a properly exposed subject any more, the subject will be a stop under exposed along with the background, so you have to dial in +1 EV comp on the flash to counteract the camera. Or you can shoot in manual, which is what I usually do, but still, it would be nice have the extra flexibility.
Now the Nikon system does a VERY neat trick, it' relays the focus distance from the lens to the on-camera flash. So let's suppose that you're focused on a subject who is 5 meters away. The camera tells the flash the camera-to-subject distance, which in the case of on-camera flash also happens to be the flash-to-subject distance, and the flash can make a quick guide number calculation and know exactly what power level to set to get a perfect exposure every time. I don't have a Nikon on which to test it, but in theory, it could do this even without a preflash, assuming there is only one light in the setup. No preflash mean much less of a chance that your subject will blink.
Now comes the big one, "zones". With the Canon or Nikon system you can set up groups, or "zones" of off-camera flashes, and control their output from the camera position. You could have your key light(s) in one group, your fill in another, and your background lights in another. On Nikon you can even add a 4th group, so hair and edge lights could be in another. Then if you want your background brighter, you just bump it up from the camera, and the controller flash tells the background group to increases it's exposure durring the "preflash talk". Hair light too hot? Just turn it down from the camera. Pentax only has "channels", which allow you to shoot in the same room with another photographer and not set off their lights. (Canon and Nikon use channels too of course.) But without zones, all lights on one channel fire at one power level, there is no control over lighting ratios.
Another maddening thing about the Pentax flash system is it's implementation of High Speed Sync. HSS, if you don't know, allows you to fire the flash at faster-than-max-sync speeds. It does this by firing a series of rapid bursts for the entire time the shutter curtains are in motion, 1/180th of a second in the case of Pentax DSLRs. The effect is the entire frame is illuminated, where as without it, you would get those dreaded back bars in your flash pictures at the edge of your frame. Now in all honesty, I don't think they're all that bothersome, you just have to frame accordingly. But HSS lets you fire the flash all the way up to the camera's max sync speed, although at substantially reduced power. In practice you get about a stop or two more usable light unless you have the flash obscenely close to your subject. So far we have discussed the problem, all brands face the same challenge with HSS. Where the Pentax system gets so frustrating is you absolutely, 100%, CANNOT fire a HSS flash off camera without having another HSS capable flash on the hotshoe. I put that part in bold because it is the furthest thing from obvious until you buy one HSS flash and try to make it work. The camera looks for the presence of an HSS flash on the hotshoe, and if it doesn't find one, it turns off the pop-up flash, the hotshoe and the PC socket at speeds over 1/180th. In other words there is no way to send a sync signal to an external flash.
Apart from those, there's third party support, now that's not directly under Pentax's control, but perhaps if they had a more serious flash system, these third parties might try to capture some of the as-of-yet untapped Pentax flash accessory market. For instance I think Pocket Wizard has largely ignored Pentax because they don't offer zone controls. So we have only one wireless pTTL solution at the moment from a company called Aoktec, but it translates light pulses into radio waves, so you still have to have a controller burst in your main exposure, even though the slave(s) are triggered by radio.
If all you do is occasionally use the pop-up flash for in indoor portrait, or slide something on the hotshoe to try and capture a vacation memory, I can understand not knowing that we are living in the dark ages of flash technology. But I think a lot of Pentaxians tend to be "natural light shooters", and I don't mean that in the I've-completely-mastered-the-intricacies-of-flash-but-prefer-natural-light sense of the word. I think many of us find flash to be intimidating, and no wonder! It's hard enough when you have all the flexibility of other brands at your disposal, but I think at some point the meager offering that is the Pentax flash system frightens many budding Strobists away from the brand entirely.
Thanks for listening to my rant, hope it's answered a few questions though.
