So I spent some time looking at the differences in video recording and displaying on both the DroidX and the iPhone4. So here are some thoughts…I going to break them down according to the device. I explain a little more in the iPhone4 description, but this is where I define some terms for the rest of the write-up.
iPhone4 Thoughts
1) The video quality is great especially since it is acquiring the image at 720p – 30 frames/second. This means that the video image is 720 lines across the width of the video display. It uses a progressive scan where the image is displayed line but line from top to bottom across the page. There is a debate whether progressive or interlaced is beter, but a progressive scan provides less visual artifacts and less motion blurring. Here is an article about progressive (the “p” in 720p) and interlacing (the “i” in the 720i). I think that the actual resolution of the iPhone4 is a little better than the DroidX camera, with less visual artifacts, but does not have the chroma in outdoor settings as the DroidX.
2) The back camera focal length is 3.85 mm with f-stop of 2.8. This is essentially equal in focal length with a 35mm SLR camera with a 30mm lens. This is a pretty wide angle lens with a wide range of view. It is a pretty good camera, but for people like me…I want the original file. If you email the file or upload it to FTP site/YouTube, it compresses the video. So, I have to dock the phone to retrieve video in the most native format. Great articles by Ars Technica and Falk Lumo about the camera.
3) When recording the video from the camera, you are not allowed to zoom. You have to use your body to zoom by walking closer to the subject.
4) Displaying on an monitor, you have to purchase the PC adapter for the iPad. 
This allows you connect to a monitor that has a PC (VGA) input. This will not allow you to play the sound on the monitor, you have to connect the earphone out to the monitor or speakers using a mini-plug. The PC (VGA) connector is $29 on the Apple.com website. But you will also need a PC (VGA) cable to complete the connection.
5) Controlling what is displayed on the external monitor is tricky. It only will display pictures/video from camera or video form the YouTube application. Displaying videos from the camera can be tricky. Sometimes if you select to play the video, it might not immediately display on the external monitor. The same with pictures, you have to be in a slideshow mode to get the monitor to recognize the images.
6) It has two cameras! This is cool, one on the front and one on the back. This allows the user to record videos or take pictures using either camera. The front camera also allows the ability to do face-to-face video phone calls. You can just touch the screen to select which camera to use to record. I have actually used the front camera to record a video and it gives me a frame of reference for what I am recording. It allows to frame yourself properly without lots of mysterious room above your head. The back camera is the one with the flash for taking photos in low light.
DroidX Thoughts
1) The video quality is great with the ability to record in 720p. It has great image quality but when displaying the video on a Flat Screen HDTV, I noticed some artifacts in high contrast areas. Basically, when you watch the video on the HDTV and walk up close to the screen, you will see block like images around high-contrast areas. But, the DroidX had better chroma quality than the iPhone4…the video did not look as washed out.
2) The focal length of the DroidX’s camera is a little wider than the iPhone4, giving the ability to capture more landscape. I had to back up some with the iPhone to capture the same image as the DroidX. Also, since I am a Mac user, I can connect the DroidX via the USB cable and navigate to find the video files. This allows me to download the native video files to edit.
3) You can zoom with the video camera on the DroidX, very cool.
4) Displaying on a monitor is done with an HDMI mini-D to HDMI cable. 
This can be purchased for $39.99 at a Verizon Retail store or $24.99 online at Verizon.com. Yeah…$15.00 extra bucks to purchase in the store! Not Good!
5) Controlling what is displayed on the external monitor is a little tricky but a great idea. Once you connect the DroidX via the HDMI cable to the external monitor; you can select a picture or video and the media plays on the external monitor screen. Then the DroidX turns into a remote control. Great idea and neat interface.