Depends on a lot of factors.
Depends on the load (is this a dedicated SQL box or does it also host applications, IIS etc).
How many instances
How many simultaneous connections
OLAP or OLTP
Will this host mission critical databases
how do you define good - do you have SLAs
how big are the databases and estimated rate of growth
Is it good to store tempdb mdf file in one drive and log file in another drive.
Daily our databases growths are 59 GB and we have only 70 GB free space out of 760 GB.
IMPT: daily 29 GB text files are uploaded into different tables in sql server and same size of old tables are deleted.
Generally, moving the temp database to a different physical drive (not just a different partition on the same drive, of course) will improve performance, as the disk seek heads do not have to wait for each other when they're on different drives (that's a simplified picture, but it'll do for now).
You probably still have it on the C: drive? It's perfectly ok to move tempdb somewhere else. I suggest a decent high-speed drive (ESATA II perhaps) not an outboard or USB drive.