What is the maximum number of records within a single custom object in salesforce.com?
There does not seem to be a limit indicated in https://login.salesforce.com/help/doc/en/limits.htm
But of course, there has to be a limit of some kind. EG: Could 250 million records be stored in a single salesforce.com custom object?
As far as I’m aware the only limit is your data storage, you can see what you’ve used by going to Setup -> Administration Setup -> Data Management -> Storage Usage.
In one of the Orgs I work with I can see one object has almost 2GB of data for just under a million records, and this accounts for a little over a third of the storage available. Your storage space depends on your Salesforce Edition and number of users. See here for details.