How common is it for people to have a name such as Hugh Hughes?

[keyboard86]

  I seem as a young child recalling a Mary Mary quite contrary?

Keyboard86

[KGarrad]

Seems to be a boy thing, and also there's a bit of a Welsh theme too?

Not quite!
Plenty of Joan Jones out there!
And a Leslie Leslie (1882)

[deebel]

A family friend with Christian name Joyce married a man whose Surname was Joyce

[tjugg]

I have a Ralph Ralph.

Linda

[Nanna52]

My grandfather was James James.  He was mostly known by his middle name of Arthur.

Although born in Australia, his parents were from Somerset.  His grandfather and an uncle were also called James.  At some stage the surname was changed to Janes in the UK, but one family changed it back to James, just to make tracing them difficult.

[jim1]

You can trace the origins back to Wales. Hugh ap (son of) Hugh.When surnames became commonplace the middle bit was dropped.So names like Hugh Hughes, Evan Evans, William Williams are quite normal if your Welsh.
I went to school with a John John.

[Hinso]

My wife's g-g-grandfather was a Walter Walter and Somerset through and through.

[GenesA]

I have a William Williams 

[coombs]

I like first names and surnames that are exactly the same, Edward Edwards, there is a 1 letter difference. I have found a George George and even a Thomas Thomas Thomas baptised when looking at a London church register once. I found his death years later and it said Thomas Thomas Thomas.