I know the DS pretty well. Even though I grew up in the age of SNES (which I can hold my own in too), the DS has been my favorite system for a while now, and it seems like we can't go into a used game store without me walking out with a DS game and Ronalopolis complaining with "I've never even HEARD of *insert game here*. Are you sure you don't just go in there and find the strangest titles and pretend you want them?" (For those new to the site, Ronalopolis barely posts, but he's my hubby.)
Besides DS and SNES, my strongest area of expertise is probably developers/publishers. For example, if you mention Atlus, I can probably name games you've never heard of that Atlus has developed/published, name which ones are rare, and give you approximate prices. Same goes for 5th Cell, Level-5, Natsume, The Behemoth, XSEED, Cing, Zeboyd, and many, many more, as well as the big names like TECMO, Marvelous, Square Enix, etc.
Story: At PAX, I saw this guy in a Skylanders sweatshirt. I thought maybe I could buy one for myself, so I walked up to him and asked where he got it. He responded that he works for the company that developed the 3DS version. When, without skipping a beat, I asked him how it's like working for Vicarious Visions, he just stared at me. Guess he didn't expect me to know that off the top of my head.