Template talk:!
I can't think of much testing I haven't already done with the version User:Alfwyn/Sandbox/! (in combination with Sandbox and previews of a never saved page) other than actually using it.
A caveat with the template is, that it shouldn't be used to seperate parameters in nested templates (completely unnecessary too) as in {{templ|{{templ2|foo}}}} (making that {{templ1|{{templ2{{!}}foo}}}}) since while working now it will break in the future (see bottom of [1]). Thís template is heavily used at wikipedia and specifically recommended for use in autolink cases [2] .
Another point might be that {{subst:!}} obviously fails to work as intended if it was necessary in the first place (well, I just mention that for completeness).
--Alfwyn 11:15, 9 March 2008 (PDT)