On the coding side of things, Lee Brimlow's GotoAndLearn site has been a growing set of invaluable video tutorials on learning AS3 and now some new JS/HTML5 things for me over the years. You can read a code tutorial and see a static page of code that someone wrote, but there's something extra special about watching the process of someone coding, and more importantly, talking out Why they're coding that way. The "Why" is something I think more unique to VBLOGs when it comes to tutorials and such. Like Programmer16 said, you get the connection and personality through a VBLOG that you wouldn't get with static posts no matter how many screenshots are there.
On the game progress/development side of things, I've really enjoyed following TreeFortress' Bardbarian dev updates. It'd be easy to throw "We added a new shop UI today with clicky things" and some screenshots on a blog, but actually getting to see the in-game video of how that UI shows up on-screen, how it behaves, what happens when you click things... When it comes to UI or just the progress of a game in general, I think VBLOGs are equally invaluable for building a following for your game before launch. People can see the game in action at whatever stage it's at in development and provide great feedback... "Why did you have to click through three menus to get to this option" for example.
On the complete opposite side of the spectrum, if you already have a solid fanbase for previous games, I've really enjoyed GameInABottle's dev blog on his new GemCraft 2 flash game that he's working on. It's all text and screenshots, but because I fell in love with his previous GemCraft games, the frequency of his dev updates has been very fulfilling. From past games, his users know the material, style, gameplay, etc and a simple screenshot showing a new menu, or a new feature with an in-depth explanation is quite satisfactory. Sure, I'd love to see in-game footage of how things work, but because the series is fairly well established, I really don't need him posting videos that took 5 hours to edit when he can just spend 30 minutes and post an update with a few screenshots.
I think Programmer16 nailed it though, it's up to the personality of the person doing the video. It doesn't matter how cool of a game you're showing off, if your delivery is uncomfortable or rambling, it's off-putting. But, you'll only get better with practice and I don't think anyone would watch an awkward "Developer VBLOG" post and write off your game or your company just for that. Jump in and try it out. It's the only way you'll know for sure! Best of luck!