Radley Balko wants left-wing bloggers to "state your limits" on the size of government (measuring by economic spending) they'd be willing to tolerate. But all the subparts (top marginal tax rate, inflation rate, debt-to-GDP) represent empirical questions the sort of which the average man on the street (left or right) isn't qualified to answer. So I'm not sure what the point of me throwing out a random figure is, rather than just deferring to progressive economists. I also highly suspect that the preferable number for all these questions is highly fact-dependent and variable over time, making it pretty useless for me to try and nail down one figure to the wall and hang it up for Mr. Balko.
It was Jon Chait who pointed out that liberals don't have any ideological commitment to big government, only an instrumental one -- we are willing to tolerate increased government spending when it leads to socially optimum results. There is no liberal who just wants government to be larger for its own sake; the debate is always tied up in some dispute over social utility. So my upward limit for the size of government is "when it stops being good to have government be larger" (needless to say, intrusions upon personal liberty are part of this calculus).