In-memory and hard-drive hybrid I'm going to start my Master of Science degree work.
My goal is to implement (and test in various scenarios) hybrid database environment: my application will communicate with two databases. One will be in-memory database and other will be standard (on hard disk) database. I want to research if this hybrid can be faster than standard database only (in certain situations).

Have you ever heard or read of someone, who tried something like this? Because if there are works like that I would like compare my results to them.

Edit:
I'm on beginning of my work, so exact topic is not cleared yet (I have something about 18 months to write it).
My main idea is to compare standard database (eg MySQL) vs hybrid (eg MySQL+VoltDB) with the same set of data, where on hybrid some tables (or maybe some columns from some tables) will be in in-memory database.
Mainly I want to compare time performance, but maybe other aspects (like administration issues of that hybrid) as well.
Microsoft just announced Hekaton which allows you to have a mix of in-memory tables and traditional on-disk tables in the same database, and seemlessly integrate the two technologies.  It will ship in the next major release.  They annouced it at the 2012 SQLPass Summit during the day 1 keynote (viewable online).