The Chesapeake Bay Mg/Ca proxy goes to late 1995 and is used in both Moberg et al  and Mann and Jones  for the proxy reconstructions up to 1980. Figure 1 below shows that its post-1980 behavior does not show an exceptional response to supposedly unprecedented temperature.
Figure 1. Chesapeake Bay Spring SST. Re-plotted from data at WDCP . See Figure 4 in article.
The Mg/Ca proxy for spring sea surface temperature "relies on the thermodependence of the uptake of magnesium into the calcitic shells of microfossils (Dwyer et al., 1995; Lear et al., 2000). Mg/Ca ratios in ostracode (Crustacea) shells are influenced by the water temperature in which the shell is secreted and the Mg/Ca ratio in the water." [Cronin et al, 2003]. The data goes up to late 1995 and does not include the warm 1998. However, it is evident that there is no unusual response of this proxy. The plot of the 19th and 20th century data looks more volatile, but Cronin et al.  do not discuss whether this is an artifact of sampling. One sees increases in volatility in the modern portion of ice cores, where the change is attributed to isotope migration. One wonders whether a similar phenomenon may be at work here.
Both Moberg et al.  and Mann and Jones  splice CRU surface temperature histories after 1980 to their proxy reconstructions and the post-1980 proxy information is not used in these studies. Jones and Mann  does discuss proxy behavior after 1980, claiming that the proxies from Mann and Jones  also show unprecedented warming after 1980. A simple inspection of this record shows that it is obviously not driving the Jones and Mann  claims. I think that I’ll show a couple more proxies and will make some comments on Mann and Jones  and Jones and Mann  in a few days.
Cronin et al. contains the following interesting short history of temperature in the Chesapeake Bay, comparing local measurements and COADs measurements, with the COADs measurements diverging on the warm side in the later 1990s. I’m not familiar enough with the temperature datasets to comment on this issue, but found it interesting.
Original Caption to Figure 2b in Article: Comparison of Chesapeake Bay (CB station 5.1, >15 m) and COADs (75.7 –76.5jW, 36.5– 37.5jN) monthly temperature anomalies 1984– 1997. Chesapeake Bay temperatures from monitoring stations for the period1984– present (http://www.chesapeakebay.net/data) and for the period 1949– 1984 from M. Olson, Chesapeake Bay Program (http://www.chesapeakebay.net/bayprogram/data/wqual/htm). Comparisons of CB temperatures were also made with oceanic SST anomalies fromCOADs data from 1950– 2000 from the NOAA COADs website (http://www.scd.ucar.edu/dss/coads) and from 1984– 1997 from LamontDoherty Earth Observatory (available at http://www.lido.ldeo.columbia.edu).
Reference: Cronin, T. M., G. S. Dwyer, T. Kamiya, S. Schwede, and D. A. Willard, 2003. Medieval Warm Period, Little Ice Age and 20th Century Temperature Variability from Chesapeake Bay. Global and Planetary Change, 36, 17-29. ftp://ftp.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/cronin2003/cronin2003.txt