I applied in the first week of January 2014 and received a call in the last week of January. I went through the first round, which was a screening with HR. It was very easy and covered basic CS questions. The interview proceeded as follows:

• Why Yelp?
• Why would we hire you?

And then a few technical questions:

• Signal for the kill command?
• Performance of a binary tree if implemented through an array or linked list?
• SQL command to move a row in a table?
• Protocol used to transfer messages in an HTTP application?
• SSL?
• Number of bits to represent octal?
• Maximum value that can be represented by an unsigned int?
• Which of the following describes an inner join? (e.g., A intersection B, A union B, etc.)

I am now waiting for the next round, which is a Skype interview a week from now.

All questions were very basic and posted here.