  We consider constraints on generalized tachyon field (GTF) models from latest
observational data (including 182 gold SNIa data, the shift parameter, and the
acoustic scale). We obtain at 68.3% confidence level $\Omega_{\rm
m}=0.37\pm0.01$, $k_0=0.09^{+0.04}_{-0.03}$, $\alpha=1.8^{+7.4}_{-0.7}$ (the
best-fit values of the parameters) and $z_{q=0}\sim 0.47-0.51$ (the
transitional redshift) for GTF as dark energy component only;
$k_0=0.21^{+0.20}_{-0.18}$, $\alpha=0.57\pm0.01$ and $z_{q=0}\sim 0.49-0.68$
for GTF as unification of dark energy and dark matter. In both cases, GTF
evolves like dark matter in the early universe. By applying model-comparison
statistics and test with independent $H(z)$ data, we find GTF dark energy
scenario is favored over the $\Lambda$CDM model, and the $\Lambda$CDM model is
favored over GTF unified dark matter by the combined data. For GTF as dark
energy component, the fluctuations of matter density is consistent with the
growth of linear density perturbations. For GTF unified dark matter, the growth
of GTF density fluctuations grow more slowly for $a\to1$, meaning GTF do not
behave as classical $\Lambda$CDM scenarios.
