We promised a few weeks ago to dedicate a blog post to the launch of other YCombinator funded companies. Last week Likebetter.com launched. The makers are good friends of Xobni. Their CEO, Bryan Kennedy, was our roommate for the month of May.

It is important to learn from the experiences of other companies. What did we learn from Likebetter? The marketing power of blogs, Digg, Reddit, and Stumbledupon is astounding. But that attention can bring traffic levels that few sites are prepared for.

Likebetter.com is a simple idea with powerful implications. They show two pictures side by side, and you click the one you “like better.” Viewing pictures this way is addicting. Five percent of their visitors remained on the site for one hour or more.

The web site uses your image choices to make predictions about you: guy or girl, age, neat or messy, and over 25 other characteristics. Brian Hawthorne their CTO has implemented a machine learning algorithm that makes these predictions.

These predictions are more than just cool computer intelligence; they are market research! Likebetter has found a really smart way to identify the demographics of their audience. Marketers and advertisers love this stuff!

Why is their method so unique and successful? Often web sites try to determine a user’s demographic by asking a series of questions. How boring. Often people don’t even enter accurate info. Contrast that with what the brain on likebetter does.

Even if the brain guesses wrong, you are compelled to correct it. This is a brilliant way to elicit demographic data from your users without burdening them with a survey.

Likebetter’s overwhelming popularity on Digg drove significant traffic to the site; to the tune of 10,000 visitors an hour. This traffic overloaded their web site. They shared some valuable discoveries with us.

1. Google Analytics is Slow – The urchin javascript is slow. Use server logs for traffic details when you get a big spike in visitors.

2. Ruby on Rails is Slow – Their old site used PHP, time tested and fast. The same couldn’t be said for Ruby. They had to kill some of their features to simply load images.

3. Use caches instead of always hitting the database – When your site is serving a few thousand images a day requesting images from a database is acceptable. When you serve 100,000 images in a day, other techniques need to be applied.

4. Bloggers are your friends – We had a pretty good idea about this one. The marketing world has changed. Bloggers WILL drive more traffic to your site than a mention in Time Magazine.

One of the best things to be said about being involved with YCombinator is the support of a community. I can’t stress enough how cool it is to make friends with 25 people with a similar love of technology and business. We share our successes, our failures, and help each other whenever we can. Getting involved with YC was one of the best decisions Xobni made.