In Reddy v. MKBS Company Limited, (Del. Supr., March 3, 2008), read opinion here, the Delaware Supreme Court  (yesterday) affirmed a Chancery Court decision, summarized here,  finding that an attempt to "cancel" shares, whether via the certificates representing those shares or the shares themselves, did not comply with statutory and related requirements. Both courts also addressed the difference between "void" and "voidable" stock.  The money quote follows:

The cancellation of those shares could only be accomplished by complying with the procedure mandated by 8 Del. C. § 242—a written charter amendment, authorized by the board of directors, approved by the shareholders, and filed with the Delaware Secretary of State. Reddy concedes that those requirements are applicable to cancellations of stock, and that no charter amendment for either MKBS company was ever effected.