Hi!
I was fascinated to work through the examples provided in the 
org-tutorials sections under Worg and really see the power of using 
eLisp as spreadsheet formula: 
http://orgmode.org/worg/org-tutorials/org-spreadsheet-lisp-formulas.html

However the use of the mapconcat function always generated an error: 
Invalid regex "Regular expression too big", even with only a few terms 
in the formula.

The offending formula was:

#+TBLFM: @2$3='(mapconcat 'identity (delete-dups (list @2$1..@>$1 @2$2..@>$2)) " ")


I experimented with variations of the formula getting the same error 
every time.

I did a search of the org-mode forum without finding any solution.

Any thoughts?

Regard