Not that I know of. It is interesting that so many use Solr though - Vufind, Blacklight, Helios (aka fac-back-opac), XC (Extensible Catalogue), Visualiser (Commercial product from VTLS).
Some commercial products use Solr as well (as far as i know eg. Summon, Primo (ExL rarely talks about that, their wording is "Primo is using lucene" but I think I understood they actually use Lucene in Solr...). Seems Solr is definitely the search engine software of choice at the moment for library applications. For good reasons of course :-).
There are some articles in classic journals on some of the mentioned discovery interfaces, but I don't know of a comparision either.
Karen, what would you like to have compared? There are many aspects I can think of (usability, technical architecture, "OPAC features", adaptability, sustainability...). I really don't like those kinds of "check list comparisions" ([ ] advanced search, [ ] relevevance ranking, [ ] faceted browsing, [ ] supports some foobla buzword [ ], ...) because the items usually are important only in specific contexts or are pretty meaningless at all (like "relevance ranking"). So what are you looking for?
Regards from Busan,