I suspect the libertarian centralist opponents of federalism are secretly upset that the EU Constitution has gone down to defeat. After all, what self-respecting, politically-correct, egalitarian libertarian could fail to support a new central state being formed that could forcibly suppress "bad" things like "opponents worrying about loss of national control and identity to a stronger, unaccountable EU bureaucracy at the heart of a superstate" and "anxiety about mostly Muslim Turkey possibly becoming an EU member". The Netherlands voters were worried about "losing control of immigration rules that have been tightened to stem an influx from Muslim countries amid ethnic clashes". Certainly any good libertarian has to favor setting up a stronger central state that can strike down "bad" laws and practices of the constituent states. Without a stronger EU state, there will no doubt be some cases where member states will get away with illiberal laws that might have been nullified by an EU Supreme Court. Gasp! How can any decent libertarian be in favor of bad national laws? Surely, we must support an ever-larger central state in order to be in favor of liberty. Er, mustn't we?
Aside: re Lew's post about the European Union Constitution allowing secession, as I noted previously, if any rich state, say France, Germany, or Britain, tries to leave, a majority of poorer states could stop it by simply indefinitely "extending" the period that the EU Constitution applies to the State desiring to leave. More discussion here.