These "active-duty" campaigns (Bill's and Aramis') sound quite interesting - though they'll require players who don't have issues with having an authority over them. However, they seem refreshing to me as the lend structure and, if administered properly, give very fun RP possibilities. To say the truth I'm currently playing in such a campaign, with my character being Solomani naval Captain. Very fun so far
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The good thing about Traveller military campaigns, as opposed to ones in other modern/scifi RPGs (Shadowrun, for example) is Traveller's comm-lags resulting in a ship's CO having quite alot of autonomy and orders being general (i.e. "go to star-system X, deal with issue Y" or even "patrol star-systems A, B and C, deal with any problem that arises").
Military/duty campaigns work best with players who don't want to deal with the economical side of things or with random exploration; the Service (Military, Scouts, Police etc) provides the gear and pays for repairs/maintainance, and you'd usually have generic orders that'll hook you into the plot.
An idea that has just poped into my mind is a police campaign. No, not planetside police (though that couldbe quite fun as well, especially in high TLs), but an interstellar law enforcement agency on the high frontier ("Texas Rangers" rather than "NYPD"). The players in such a campaign will have a Type-T Patrol Cruiser at their disposal, as well as enough NPCs to fill the roster besides them; they'll have to patrol a subsector of deep frontier, deal with pirates and planetside criminals; and such a campaign would be served well by having some kind of "criminal mastermind" or syndicate as the recurring villian to be defeated at the end.