[btrask]

LSM trees are ideal for posting lists, because every time you add a new document, you need to touch potentially hundreds of different lists. LSM trees are able to batch all of these writes together. That's why Google originally developed BigTable, AFAIK.

[teraflop]

In fact, Lucene (the library behind Solr and Elasticsearch) is basically a special-purpose inverted-index-as-LSM-tree database engine.