PubSub once held so much promise... It was the first real 'future search' product to gain traction and it was an innovator in the area of custom RSS feeds. The somewhat clumsy term I've used for that is Topic/Tag/Remix Feeds and here's what I said about it back in January 2005:

"Tools will evolve to let people easily set-up personalized searches for information relevant to them and subscribe to the results - using, you guessed it, RSS! Google will probably be the front-runner (see this video for a hint to the future - thanks twdanny for the reminder), PubSub will be another, current players like Bloglines and Technorati will be in amongst it, and who knows who else."

As well, I thought PubSub was one of the leading companies in filtering feeds - the next layer up from aggregation. But unfortunately for all their promise, PubSub never quite lived up to it and services like Google News and Technorati have taken the limelight instead. Technorati has had its technical issues (which remain to this day), but one thing they've always done very well is the UI. Which is where I feel PubSub has let itself down, because their UI has always been a bit awkward and geeky. Technorati has also proven itself to be outstanding at PR and drumming up publicity about itself. PubSub never really got that knack, despite Bob and others best efforts to talk up its technology. If anything PubSub has been too tech-centric, whereas Technorati reaches out to 'the people' (with its tags PR blitz and the 'A-List Person's Favorite Blogs' feature, for example). 

However it's precisely because PubSub has always been very forward-thinking about web technology that made me like it and thus makes me sad about its demise. PubSub was into topic mapping circa 2004, when few other mainstream RSS companies were. PubSub was also one of the instigators of the Structured Blogging open source project. Indeed I worked with them - via Broadband Mechanics - on the recent website re-design (SB is a separate entity now, so isn't in danger of sinking with PubSub).

Their technology nous has always impressed me and at the end of 2004 they came very close to being named my Most Promising Web 2.0 Company of 2004. I gave that honor to Feedburner in the end, but here's what I said about PubSub (Dec 30, 2004):

"...PubSub has been building a technically very sound service mostly quietly in the background (but that's about to change in '05, by the looks of it)..."

That 'by the looks of it' pointed indirectly to PubSub's 2005 resolutions, which currently is a File Not Found page. That about sums up the situation, I'm afraid. Whereas Feedburner and other promising startups I mentioned at the end of 2004 (e.g. Bloglines, SixApart) have gone on to greater things, PubSub lost its way and the end looks imminent. I really hope they can somehow turn things around and get rid of the 'political' monkey on its back, because I know they have the smarts and the people to achieve success.