Well lets say you are operating at small scale and you can reduce your 32 servers sucking 20 kilowatts to 4 appliances sucking 5kW. Much reduced footprint, power cost, admin cost (at small scale your per server cost is going to be higher than the large scale guys). Plus someone else will have done the integration and tuning work.

I think even on a small scale, or perhaps that should be especially on a small scale, people could profitably look at the mysql/nosql/memcached (the latter optionally with persistence via flash) from some of the appliance vendors.

I have no financial interest or direct experience, but the data sheet on this:

http://www.schoonerinfotech.com/datasheets/Schooner_DS_Memca...

looks worthy of a closer read.