If you're using the same shared storage unit, having a seperate partition for the TRANSACTION logs isn't going to make a massive difference performance wise because it's still using the same IO.

However, saying that, it is probably still a reasonable plan to do this to :

a) Keep things tidy

b) Prevent Fragmentation (which WILL affect performance!)

The latter can get to be significant if you have both the T-log and DB files on the same partition, especially  if you have AutoGrow on both the files and didn't deploy the initial database as an xGb file to start with. The 2 files start intermingling and the Defragmenting tool shows the drive to be the "Red Sea" !? If this does occur, you have the additional problem in that the defrag tool may not be able to rectify the problem because SQL Server has these files locked!

Cheers

Mark