There have been very few people whom I've worked with at past jobs throughout my career that I would actively try to work with again, and Sergey is definitely at the top of my list.
Sergey and I worked together at RTC/Wunderman on a variety of UX design and development projects, and he was consistently organized, solutions-oriented, collaborative, innovative, and last but not least -- great to work with. He uses a firm understanding of the primary business goals to drive his decisions and recommendations about implementation, even in cases where a change in direction is necessary.
Sergey is knowledgable, not just about details as they pertain to his own discipline, but also when it comes to others, including development, technology, strategy, and marketing. When working with Sergey, you know things will not only get done, but done right. He's a sponge when it comes to knowledge, and is proactive about sharing it.
Sergey is a great communicator, whose expertise and success gained him the trust and respect of his co-workers and clients. I would not hesitate to recommend him for employment (even if it has to be at company other than my own).