How many people have it installed? How many sites have it enabled? What apps/sites exist & are popular that wouldn't be useful/popular without gears? What apps/sites exist that are replacing installed apps thanks to gears? For an example to count it needs to include more people outside the top 5% of internet users.
Personally I wouldn't call it a dud yet. It's mostly for readers, online office apps & calendar. These are used mostly by the top 5% anyway, so it'd be hard to take a stab outside that segment with Gears. Mail is the online app that has penetrated, but those that need off-line mail generally have a client installed already. It'll take time to move them since 'you don't need to install a client' isn't an incentive if you already have one. But this is a pretty big change they're trying to pull off. A lot of people are going to have trouble even finding gmail without a Google search.
Like I said, I wouldn't call it a dud. I wouldn't call it a success either. Like the post says, Chrome might bring it all together.