Critical reviews back when it first hit the US shores were quite positive from memory (as is typical of successful britcoms), but as Jan Mixon points out, the American remake (which shared little more than the overall concept and series title) did extremely poorly (why is a much more involved question covered here: Why do American versions of British programmes tend to translate poorly to American culture?).
Similarly, DVD sales seem to be quite low (though ratings at sites like Amazon are very high).
The original series seems to have aired at some point in the US on BBC America (which had very low market penetration in the early-mid 2000s), as well as being syndicated on a fair number of local PBS networks (who historically have purchased the majority of broadcast rights to british TV (but especially sitcoms). Getting viewership numbers for either is a task beyond my resources.
From my personal experience, anyone I know here who has watched (willingly) at least one british sitcom title, is at least aware of Coupling – either seen it, or heard that they should. It's a fairly common netflix suggestion when people inquire about a good date-night show. But yeah, not a big scale moneymaker, more of an evergreen long-tail sleeper like 'Allo, 'Allo.
deano.com 