Is there any difference between 'source <path>' and '. <path>' ?

[Manish Jain]

Hi,

I used to be under the impression that 'source <path>' was fully 
equivalent to '. <path>' : both executed <path> under the current shell. 
(At least under Bourne shell derivatives)

But a few days back, I came across an instance where source fails while 
invocation with period succeeds.

So I feel inclined to ask whether the 2 mean the same or not ?

Thanks for any help.
Manish Jain