The number of nodes supported is not limited by Oracle, but more generally by the clustering software/hardware in question.

When using solely Oracle Clusterware: 63 nodes (Oracle 9i or Oracle RAC 10g Release 1) With 10g Release 2, the maximum nodes is 100
When using a third party clusterware:
Sun: 8
HP UX: 16
HP Tru64: 8
IBM AIX:
* 8 nodes for Physical Shared (CLVM) SSA disk
* 16 nodes for Physical Shared (CLVM) non-SSA disk
* 128 nodes for Virtual Shared Disk (VSD)
* 128 nodes for GPFS
* Subject to storage subsystem limitations
Veritas: 8-16 nodes (check w/ Veritas)
For 3rd party vendor clusterware, please check with the vendor.[@more@]