@Tracy We sync accounts in SF with customers in NS, and contacts between both, but we funnel them through an internal database of customers and contacts. We use DBAmp for read-write access to Salesforce, and SuiteAnalytics Connect (ODBC) for read-only access to NetSuite. Any writes to NetSuite have to hit a Restlet, though we did briefly use a product called CDATA that had read-write access for NetSuite.
The benefit of this is that at all times we have copies of both systems, and we can compare them locally which is quite efficient, but requires a certain level of internal database expertise and maintenance.
If you are looking to bypass that and have the two systems sync up directly, that is likely where Boomi or Celigo would be the most useful.