ProsSpeed - when I first got this, I set it up and printed a document. It printed so fast, and I wasn't watching, that I didn't realize it had printed! I did that two or three times before I realized what was happening.
Cost per page - toner is pricey like it all is, but the yield is good so the price per page is low.
Built in duplexer - I like to print duplex pages. It just makes it easier to handle - particularly larger documents. Cost savings and tree savings are an added bonus. When you configure lesser printers, Dell or otherwise, with an add-on duplexer, you start puching the price up to the point where you can get the speed of the 5110cn almost for free.
ConsIt is pretty noisy. If you are in a quiet office or print much, that could be a problem.
I print mostly text and drawings and it's fine for that, but there are probably better choices for photo printing.

I'm not sure it handles things like envelopes very well. Limited paper handling.

Review:I tested it with 2 point type - it was legible (with a magnifying glass)