I am trying to find information on the Tibetan name Dechen. I am after
meaning, usage (boy or girl or both - I've seen both but want to be
sure); and pronounciation.

kerso...

While every usage of the name Dechen which I located is
for a female, the meaning of the name itself seems to 
be neutral enough that it could be used for a male.

The meanings I found were consistently synonymous with
each other:

Health and Happiness

Bliss or Great Joy

Great Bliss


'Health and Happiness' is the meaning given in two
independent directories of baby names.

The ComeParty website in New Zealand lists Dechen as
meaning 'Health and Happiness' in its directory of 
Girls Biblical and Spiritual names:
http://www.comeparty.co.nz/bsnames.htm

BabyNamer.com likewise has Dechen listed with the
meaning 'Health and Happiness' in their directory of
Ethnic origin Names -> Tibetan Names -> Girls Names:
http://www.thebabynamer.com/show_middle_name.jsp?mid=13970&id=13985


The Sakya Dechen Ling Meditation and Retreat Center
has a pdf file in which it gives the meaning of its
name and its purpose:

"The name Sakya Dechen Ling means 'blissful Sakya place'
 (or 'Sakya Place of Great Joy'). The emphasis of the 
 Center is on the practice of women in Tibetan Buddhism"
The pdf file is here:
http://www.sakyadechenling.org/assets/docs/membership.pdf

Or you can view the file in your browser in Google's cache:
http://66.102.7.104/search?q=cache:FwVyvhNkupkJ:www.sakyadechenling.org/assets/docs/membership.pdf+Tibetan+name+Dechen+meaning&hl=en&lr=lang_en


And finally, in Chapter One of 'Women of Wisdom' by 
Tsultrim Allione, on the Snow Lion Publications site,
a spiritually gifted female discloses to her disciple:
"He named me Dechen Khadro, which means 'great bliss dakini.'"

It's a little less than halfway down this page:
http://www.snowlionpub.com/chapters/wowi.htm


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Additional information may be found from an exploration of
the links resulting from the Google searches outlined below.

Searches done, via Google:

Tibetan name Dechen meaning
://www.google.com/search?q=Tibetan+name+Dechen+meaning

Dechen meaning happiness Tibetan name
://www.google.com/search?q=Dechen+meaning+happiness+Tibetan+name