Working for a technology startup can have its challenges.  There are lots of insecurities associated with the business aspects of a startup, but it is certainly invigorating to work at the edge of what is possible in your chosen professional field.  I do not think I have ever enjoyed a job so much.  I am senior enough in my career to be given ownership of an element of the product we are developing that is critical to its success.  It is a hard problem that I cannot solve on my own, but I have access to some very smart people to help me.  I think one of the things I like best about being a senior engineer in this domain is that I know when I need help from someone else and I am not too insecure in my knowledge to ask for it.  Who knows how it will turn out.  My technology is not the only critical element of the system.  Even if I succeed beyond my wildest expectations, the product could fail.  All I know is that it is pretty wonderful to be at this point in my career and to not only love my work, but to be valued by my co-workers and management.