At my work place we have used the Infobright Community Edition, http://www.infobright.org/, for a while now, and with great success.
For those who don't know what Infobright is, I recommend that you take a look at this page, What is ICE?, ICE stands for Infobright Community Edition, which is the open source version.
One of Infobrights great strengths are compression, which is top-notch. And for certain analytic queries it performs very, very good.
But there are certainly room for improvements, fx. as Infobright uses its own optimizer, not the default MySQL optimizer, certain queries aren't optimized very well yet, and some aren't supported at all. Unsupported queries will fall back to the standard MySQL optimizer, which doesn't work well with Infobright tables.
Also they are very slow to implement contributed patches, because of this, I've decided to post patches in this blog. Patches which are committed to they're bug tracker, but also patches which are developed specifically for use at my company.