Hmmm. A scan of wikisource shows a preponderance there of the "by" construction. Also, a possible qualitative difference - "in leaps and bounds" seems mainly to describe a way of moving. As well, I think both existing entries are missing a sense of change happening in large discrete bursts (as opposed to rapid, continuous change).
I note that leaps and bounds is defined as adverb. Simple deletion as proposed effectively means parsing "by leaps and bounds" as "by <adverb>" (to become again an adverb). If not an abverb, is "leaps and bounds" idiomatic? Pingku 13:09, 11 December 2010 (UTC)
As by leaps and bounds is occasionally used after forms of "be" in this sense ("The improvement is by leaps and bounds"), I have made the PoS Prepositional phrase. I have added leaps and bounds (“dramatic improvements”). That "by leaps and bounds is in the US (COCA) by far the most common collocation is a good reason to make it a redirect. The great variety (and reasonable frequency) of other collocations is an excellent reason to make leaps and bounds the sole real entry. The UK-US difference in relative frequency of the "in" and "by" collocations is the sole valid rationale for keeping both in leaps and bounds and by leaps and bounds as entries. This could also be handled by a usage note at leaps and bounds#Noun, with the two redirects. (BTW, the "in" form is not dramatically more frequent than the "by" form at BNC. DCDuringTALK 17:21, 11 December 2010 (UTC)
See Talk:by leaps and bounds (IP poster). Mglovesfun (talk) 15:38, 2 April 2011 (UTC)
Redirected.—msh210℠ (talk) 22:39, 18 July 2011 (UTC)