Problem with using DSLR for filming is you need a lot of other parts in order for it to be worth it:
- External mic as the internal one peaks like crazy and catches wind like crazy
- Tripod with video head if you are doing any filming, tripod even just to it stays level as it can be pretty front heavy depending on the lens. And if it's not secure, you will cry as your DSLR drops on the floor.
- Lighting, even with HD footage, if your DSLR body is a lower one (550D for example) the sensor in low light is horrible, so you need adequate lighting or studio lighting.
- Glass/lens. The kit lens that the cameras come with aren't fantastic. They don't autofocus (if you don't have a camera man). Also they are cheapy feeling and the quality is shoddy. So you are going to probably have to invest in a fast prime lens if you want to upgrade the video quality.
That said, if you are willing to put in the investment for those things, you will truly unlock the potential of filming with DSLRs. Same goes with using it for photos, then the price goes up more haha.