I've done a little analysis of the templates in the last en.wikipedia data dump to look for these Evil Templates with Incomplete Tables.
The entire enwiki data set contained 55,921 template pages as of May 18.
13,310 templates appear to contain complete wiki tables. 493 appear to have a wiki table start "{|" but no end 883 have an end "|}" but no start 1717 contain table rows "|-" but neither start nor finish
2,218 templates appear to contain complete HTML tables. 34 have a <table> but no </table> 39 have a </table> but no <table> 274 have a <tr> but neither <table> nor </table>
I haven't looked up usage to see whether these are under- or over-represented in use.
The lists of templates matching the above criteria, the Jython script I used to run the counts, and a pre-extracted set of templates for those of you who don't want to download a 2-gigabyte file just to get 9 megs of compressed templates are at http://leuksman.com/misc/templates/
-- brion vibber (brion @ pobox.com)