From the Postgres FAQ:

4.6) What is the maximum size for a row, table, database? These are the limits:

Maximum size for a database? unlimited (60GB databases exist) Maximum size for a table? 16 TB Maximum size for a row? unlimited in 7.1 and later Maximum size for a field? 1GB in 7.1 and later Maximum number of rows in a table? unlimited Maximum number of columns in a table? 250-1600 depending on column types Maximum number of indexes on a table? unlimited

Of course, these are not actually unlimited, but limited to available disk space and memory/swap space. Performance may suffer when these values get unusually large. The maximum table size of 16TB does not require large file support from the operating system. Large tables are stored as multiple 1GB files.

The maximum table size and maximum number of columns can be increased if the default block size is increased to 32k.

Jonathan