No but a quick google
Without looking I’m guessing it uses COM to talk to ADO which I suspect
would add some overhead.
This http://www.loudthinking.com/arc/000534.html being the first article
at the top of the search is interesting too.
Unless you have a specific need for MS SQL Server (Legacy DB etc.) then
consider one of the open source alternatives (MySQL, Postgres etc.) and
make your Rails app cross platform, opening up greater