Viewfinder
Canon claims that the viewfinder for the 50D provides about 95% coverage, which seems about right; the captured images definitely did not have the same edges as the viewfinder image. This is a little annoying and makes composing shots rather awkward, as you can't line up objects against the edge without taking a shot and looking at on the LCD screen to see if you got it right. Otherwise the viewfinder is fine; images looked clear and bright and there is a good selection of information presented along the bottom of the frame that tells you the current settings, including the shutter speed, aperture, ISO setting, etc.

The viewfinder on the 50D has only 95% coverage, meaning
that your photos don't turn out exactly like what you see
LCD Screen
The big, bright 3-inch LCD screen is definitely a huge improvement over the 40D. Although it is the same size, it is definitely much clearer and brighter, because the screen resolution has jumped substantially, from 230,000 pixels on the 40D to 920,000 pixels on the 50D. This makes the images on screen seem much sharper and brighter.

The LCD screen of the 50D is the same size as
its predecessor, but boasts much higher resolution
Flash
Some higher-end SLRs skip the built-in flash, but the 50D has one built in above the lens mount. The flash pops out when you press the dedicated button. It doesn't travel particularly far, though, so red -eye may be an issue. Fortunately, the camera includes red-eye correction in the form of a number of pre-flashes which make the iris close. The guide number for this flash is 13, unchanged from the 40D, which should be good for about 13 feet of coverage.

The relatively high flash position helps minimize red-eye.
Lens Mount
The 50D has a standard Canon EF lens mount, which will work with both EF and the EF-S lenses that are used on the lower-end Canon SLRs. But if you use EF lenses on the 50D, you will get a smaller angle of view from what you are used to with a 35mm film camera because of the smaller sensor size (this is also often referred to as the crop factor). While this is great for telephoto lenses (as you get a free 1.6 x boost), it’s not so great for wide angle lenses, as the field of view will be reduced. Canon’s EF-S series and L series professional lenses are built with this in mind, though. UPDATE: this section of the review was updated to clarify the explanation of the crop factor).

The EF lens mount can work with both EF and EF-S lenses
Connections
The 50D has a decent set of connections, which should cover most eventualities. There's a power port (which allows you to charge the battery inside the camera), a remote control port (which allows for wireless remote controls), a USB port and two video outputs: an analog video and a mini HDMI port for connecting to a HDTV.
A wide selection of ports provide everything from fast
computer connections to viewing on a HDTV
Battery
The battery of the 50D fits into the hand grip from the bottom. On some cameras, access to the cover for the battery port is blocked by the tripod if the camera is mounted, but that's not the case on the 50D, as the battery cavity is well away from the tripod socket. The battery itself is a 1380mAh model, which is significantly less than the 1800mAh of the 5D Mark II battery. If this translates into a lower battery life remains to be seen, but we'll be looking into this as part of our full review that will be coming soon.
The battery of the 50D hold 1380mAh of charge
The battery fits neatly into the camera's hand grip
Memory
The 50D uses CompactFlash cards to store images, skipping the SDHC cards that are becoming increasingly common. This will be welcomed by anyone who has a stockpile of CompactFlash cards. The door that covers the slot opened very easily, and swapping the cards out should not take long.

The 50D uses CompactFlash memory cards
Other Features
Dust Removal and Mapping – The 50D includes an ultrasonic dust removal system, which uses an ultrasonic vibration to try and knock dust off the sensor. If that doesn't work, the system can map the dust and remove it using Canon's own software. It does this by asking you to take a picture of a white object, then working out which dark specks are dust on the sensor. However, this only happens in the software after the images are downloaded, and it only works with Canon's own image editing software.