During developing for my project panFMP I had the following issue:
I have a cache for queries (like Solr has, too) for query results. This cache also uses the Sort/SortField as key into the cache. The problem is, because Sort/SortField does not implement equals() and hashCode(), you cannot store them as cache keys. To workaround, currently I use Sort.toString() as cache key, but this is not so nice.
In corelation with issue
LUCENE-1478, I could fix this there in one patch together with the other improvements.