Here is something I said about metasearch in these pages some time ago ....
The issue is that libraries have to manage a range of database resources whose legacy technical and business boundaries do not very well map user preferences or behaviors. The approach has been to try to move away from presenting a fragmentary straggle of databases to bundling them in various ways in a metasearch application, sometimes in one big search, sometimes in smaller course or subject bundles. The issues here are well-known, not least of which is that libraries typically have limited control over the performance of the target databases. [Lorcan Dempsey's weblog]
And elsewhere ....
It is for this reason that I wondered a while ago if it might make more sense to attack the boundary issue differently, by working on business and technical approaches which would result in fewer, larger resources to search. This would reduce the complexity of boundary spanning by pushing data integration and other issues upstream. At the cost of putting more burden on the search system to make discriminations that have been lost. It does also raise the question of how much difference is useful. [Lorcan Dempsey's weblog]
It has been interesting to see the trend towards the type of consolidation I discuss above continue, consolidation of metadata and of metadata and full-text.
My sense is that Google Scholar accelerated this development, even if the level of Google's ongoing investment and interest is not clear.
Emerging service examples are Summon from Serials Solutions and the Ebsco Discovery Service. And I should mention that OCLC continues to add data sources to Worldcat.org as part of its goal of being able to fully represent library collections.