SQL2008R2 cluster w/ several Named Instances -- shared storage best practice?

Planning four node SQL2008R2 cluster; three named instances.  Each named instance requires exclusive use of a drive letter on shared storage.  Does the names instance need all it's files (data, logs, tempdb) on that exclusive drive?  Or can it use a drive shared by all 3 instances.  E.g. U:\SQLBackup\<instance-name>\...

Thanks,

Bob