(2011-07-10) Lemeur Pivot Vs Disposable Startup

Loic Le Meur of Seesmic thinks that having a "disposable Start Up" mentality (like Caterina Fake?) is immoral. His most recent Pivot was 2011-02-15-SeesmicSalesforceSocialCrm. How big a pivot defines a totally new venture, and what are the pros/cons (for employees, users, shareholders) of bringing along the legacy vs starting fresh?