Under the provisions of the original Digital Home Recording Act, anyone who copies a DVD is protected from suit: in effect, it is not the end-users fault that the government-approved serial-copy protection scheme used in DVDs is ineffective. However, with the advent of the Digital Millennium Copyright Act, the picture is less clear. Fortunately, the U.S. Copyright Office Summary of the DMCA states: "Section 1201 divides technological measures into two categories: measures that prevent unauthorized access to a copyrighted work and measures that prevent unauthorized copying of a copyrighted work. ... As to the act of circumvention in itself, the provision prohibits circumventing the first category of technological measures, but not the second." Thus, using DeCSS (or other CSS circumvention tool) is not prohibited or rendered criminal by the original amended copyright law, AHRA, DHRA, or DMCA. However, the DMCA does seem to obscure the protection from suit provided by the DHRA.
Note, however, that the DMCA does reaffirm the DHRA's provisions which make producing, distributing, or importing 'devices' (which includes software) with the intent of subverting serial-copy protection schemes subject to criminal prosecution. Thus, the writers and distributors of DeCSS and the like are subject to sanction.
Making an electronic copy of a copyrighted work, even if one were protected from suit, may be further restricted by the No Electronic Theft Act. The act sets a threshold level after which any infringing activity becomes criminal -- I think it might be $1500 within a 180 day period. Thus, the law suggests an individual could copy 40 movies every six months without the acts being considered criminal.