When I reviewed Yedda before Yaniv, CTO and co-founder of Yedda contacted me with more details about Yedda. When I reviewed Yedda, I did not see all fatures as some are less obvious then others, but can still be significant :

Although several people asked on Yedda why and how Yedda is different from Yahoo Answers, no answer has been posted to this question. And frankly, I don't see the added value either.

Yaniv was kind enough to point out the differences I was unable to find at that time :

The most obvious differences are the fact that we use free form tagging of questions and people, the fact that you have no limitations on number of questions or answers and you don't have to understand a somewhat-complex scoring system, that you have as much space as you need to ask or answer (no limitation on number of characters...), and that you can format your text, use rich media, images, links, etc.

But it doesn't stop here.
When we started designing Yedda, the goal we set to ourselves was to build a knowledge exchange service that uses a scalable model - one that can handle questions from the entire range of human knowledge (up to and including the long tail of knowledge - the somewhat niche, obscure topics on which knowledge is hard to find), without creating "white noise" for the people using it (e.g. flooding people with questions they don't care about just because a certain topic is hot right now).
To meet this goal, we've created several unique technologies:

- Semantic analysis of the question text allows us to

1. Suggest question topics (tags), instead of asking the user to choose from taxonomies or topic trees

2. Find already-answered related questions (e.g. automatic, personalized "FAQ" generation for each new or old question)

3. Match questions with people, to find the people with the most relevant knowledge for each question

4. Aggregate additional information from knowledge sources such as related blogs, books etc.

- Proactive question distribution (a.k.a Always-Fresh Questions), which:

1. Invites relevant people to answer questions

2. Continues to monitor the question status and strives to get an answer (preventing new questions from obscuring older ones (which is one of the biggest issues for bulleting board type services like yahoo answers)

3. Find interesting questions for you based on your knowledge & interests, reducing the amount of white noise and increasing the yield on one of the most precious resources on the web right now - people's time and attention

These tools use a learning mechanism which allows them to adapt to the way that people actually use Yedda, by learning new topics, associations and relationships, and usage patterns. Together, they create a highly personalized experience for the people using Yedda.

All in all, he's made a clear case for Yedda. I obviously missed out the existance of this technology within Yedda, of which I think could be groundbreaking.