Geodog has summed up a lot
One of the most striking developments in the web over the last year has been the sudden popularity of sites like Furl, Flickr and Del.icio.us, where users can categorize the data or photos they save with keywords, more colloquially called tags. Everybody in what Kellan has called the Internet chattering classes has been talking about tags, and a word for them, folksonomy, has even been coined, discussed and debated. Even Mr. Metacrap himself has signed on as an advisor to Flickr, and can be found on Flickr happily adding metadata to his photos.
I’ve always been reluctant to rely on someone else to store my data. I tried each service soon after it was released, but didn’t find any of them compelling enough to use on a daily basis. Furl I liked, but I was nervous about having all my data stored for me on the net by a company without an obvious business model, and then I found a better way to store data locally using Slogger. Del.icio.us I tried but couldn’t make heads or tails of until Joshua Schachter explained it in person at ETech 2004. Flickr I tried at the same ETech, but at the time I was blocking Flash in my browser, so all I ever got was a blank screen. So much for being an early adopter.
However, I have recently started to use Flickr and Del.icio.us on a regular basis. Why? Because they turn out to be great ways of following a conversation on the web. I display the RSS feed for my Del.icio.us subscriptions on one of my personal portal pages, and it updates hourly with what other people have bookmarked about topics that interest me. I couldn’t make the John Battelle’s Web 2.0 conference this year, but in addition to reading the blog coverage and press coverage, I searched Flickr’s web20 tag and got a good idea of who I know who was there.
Read the whole thing, as the saying goes.