Logical Drives - I/O aside, does SQL Server care? I'm one of those Accidental DBAs. Engineer at a medium sized company who worked for years to work without a DBA. We've since hired some (at my recommendation) and they're great but I'm trying to find the answer to a conversation I'm having with one of them regarding storage. 

Here's the high level question: We're on an enterprise level EMC SAN a large shared pool of mixed drives for SQL Server and we tend to have good I/O performance. Data, Logs, and tempdb all exist on "S:". 

So, does SQL Server "care" or benefit in some way from having multiple logical drives for it's different data types? I'm currently operating under the assumption that the answer is "No" but the DBA seems to think that SQL Server makes "better decisions" with separate drive letters, though he can't give me an example at the moment. 

I can see the benefit from a storage space management perspective and of course if you give a logical volume it's own spindles on the San you might see some performance ... but simply giving SQL Server a new drive letter to work with?
If you are able to segregate drives so they use dedicated communication channels to the drive (D: has it's own channel, E: has a separate channel, etc.), then I believe you may be able to achieve some gains.  If the different drives all go through the same channel to the storage then I don't think it will have an impact.

Whether or not you can segregate the drives depends on your environment (VM/Physical, storage, host, etc.)