Hi,
I am using the 5400HS for quite some time already and I have to say that I am really satisfied with the results this flash and my dynax 9 combi gives. Seldom have to worry abt flash exposure (bounce or no bounce or bounce card etc) as long as after each shot, the "flash OK" signal comes on. Of course, you must be aware of the situation like wat Vader pointed out since the TTL works through the camera meter and can be fooled and thus have to apply the appropriate compensation.
When bouncing off the ceiling, judge the angle you bounce. If not right, some light might be thrown behind the subject and this might cause only the top part of your subject being lighted up only. Overexposure of direct flash can be due to you being too close to your subject (don't forget the 5400 is quite a powerful flash) or it can be the situation, i.e. the overall view might be rather dark which fools the metering.
Just want to add something which occur to me suddenly when a friend ask me some flash questions ... correct me if I am wrong. If your camera doesn't have flash compensation but only exposure compensation, exposure compensation can be used for the flash as well (since it affects that as well in Minolta cameras). Now, you might ask, won't that affect the amient exposure. Yes it would. But if your entire view finder is mainly the subject within the flash range, then it wouldn't matter. If not, switch off the flash, take the metering of the background in manual mode and fix the aperture and shutter, switch on the flash, you can then make exposure compensation if you want (this won't affect the ambient exposure since you already fix the aperture and shutter), and your flash will fire according to your compensation.
Oooops, this post getting long .... but hope it helps.
Jerry