A bit of browsing found that nearly all of the standards orgs that one would expect to have copies of the SI definitions want money before they'll let you see a copy. I also found quite a number of examples of college course material in which the profs made some rather vague, misleading, and sometimes outright wrong statements about the MKS (SI) system, but that's probably to be expected. Some of them appeared quite old – like me.
US NIST SI is the United States Department of Commerce, National Institute of Standards and Technology, NIST Special Publication 330 which is the "United States version of the English text of the seventh edition (1998) of the International Bureau of Weights and Measures publication Le Syste`me International d'Unite´s (SI), including Supple´ment 2000: additions et corrections a` la 7e e´dition (1998)." Free .pdf, 814 KB, 77 pages, if anyone wants a download. The next revision won't be until 2007.
I find that Shanghaiceltic is probably illegal, although that may depend on where he's doing the calculations:
3rd CGPM, 1901 (CR, 70): declaration on the unit of mass and on the definition of weight; conventional value of gn† … 3. The value adopted in the International Service of Weights and Measures for the standard acceleration due to gravity is 980.665 cm/s2, value already stated in the laws of some countries.
980.665 cm/s^2 would be 9.80665 m/s^2, in a country where that legal "standard local acceleration due to gravity" is defined. 9.8165/9.80665 = 1.00100442, or a 0.1% error – very sloppy (tsk, tsk, tsk).
There is sufficient variation in local "g" to require correction in precise calculations, but for almost anything I can think of on the earth's surface 9.8 m/s^2 should be close enough (9.81 if you're fussy). It should be noted that the definition of a "standard g" has absolutely no significance within the basic SI system, and was inserted only to clarify the "kilogram weight" (or kilogram force) unit still in use in 1901. While the concept is still okay if your just buying a lump of lard, "kilogram force" is a denied, abrogated, prohibited, illegal, unlawful, disreputable, and horribly offensive notion in "scientific" work, and should never be used.
The legal definition of a local "g" has no significance if you're using a true "balance" scale, since you compare mass to mass, and variations in local g affect both masses equally. If you use the constant to calibrate a spring scale (not legal for trade in most US areas) you would "get more for your money" by buying at high altitude – but not much.