When I'm in work or dealing with other people in general I tend to be cheerful, smiley and generally good humoured.  I build up a great relationship with clients and their staff which really makes my day to day work more enjoyable (I'm an accountant).  I know that if I give them a call and am pleasant and they know they can be themselves with me that it in some way cheers them up and also makes me smile when I get off the phone...seratonin levels boosted on both sides I guess!  One colleague actually claims that I 'flirt' with one of the bank managers when I'm speaking to him on the phone.  All I do is chat while working through the more mundane tasks and if we have a laugh in there...all the better.  

I've always been a fairly cheerful person...but sometimes I can feel very down and feel like nothing can improve, that I'll never get past certain goals...and at the same time I know it's not true...and then there are times when I can be in such a great mood that I have to watch what I say because I know that my 'giddy' mood will probably let me say something I wouldn't normally say and I'll regret it...thankfully this does not happen when talking to clients!

I can see where the levels of seratonin etc could be a hereditary factor...but the experiences of life play a huge part in our levels of happiness.  Like a lot of other things in life I'd say it's a mix of everything that makes us who we are.

I agree...money doesn't buy happiness...but it certainly improves people's moods.  Just look at people before and after payday...specially in January. Our payday was yesterday...there were lots of special lunch treats and people meeting up with friends this evening and over the coming weekend...all conducive to creating happiness somewhere for some or all of them.

We are all in the gutter, but some of us are looking at the stars. Oscar Wilde