I was driving to work this morning thinking about how much I love working at a startup company (and always have).  I think there are a few unique characteristics about startup company

Every Effort Matters - No matter what I do today, whether it's adding some Web site content or finding another client service manager, everything I do makes a noticeable impact on the company.  Every day, when I leave work, I feel like I got something done and have driven the company forward.

Contrast that to when you leave work at a big company.  No matter what you do, the big company will still be a big company.  If you stop showing up forever, the big company will be just fine.  I have a hard time thinking in those terms.

Lottery Ticket Upside - Of course this depends on what type of startup you do, but particularly with Web startups (which is what I do) there is always the opportunity that the company will scale quickly and sell big.  I think of this as a "lottery ticket upside" that many startuppers can appreciate.

The idea is that someday in the future, there may be a huge exit that you just can't see today.  You work like crazy, sacrifice everything, and hold on to the hope that one day, you'll be beaming ear-to-ear on the cover of Forbes with your newfound payday.

Stuff Gets Done (Now!) - If I had to pick my favorite of three, though, it would be that stuff just gets done.  Unlike the ridiculous bureaucracy of a big company, at a startup company you just do what you think is right. 

At Go BIG if someone has a good idea today, we just implement it.  We don't sit in committees for a long time and debate it.  We don't work through managers or long project management plans.  We just get it done.

I'm sure there are a lot more and I look forward to hearing them.  Let me know what else should make the Top 10.