Well according tho Cup OF Wonder... Ian says this about the whole song...

    "Holiday guilt. Having a simply wonderful time. Wish you were here, but sort of glad you're not".
      * Ian Anderson in the album booklet.

      "The song 'Postcard Day' is really about the point in mid-holiday when that sense of guilt comes upon you and you think 'God, I'd better send some postcards home, cos if I leave it to the end, we'll get home before they do' - which rather negates the point."
* Ian Anderson; from the Papillon Press Release "The Secret Language Of Birds"

So it would appear that the dude in the song is ON holiday...

Postcard Day

My eyes are wide circles above cheek bones on fire:
pale hand gripping my pen.
Rounding up to the zero, adding infinite fractions,
letting nine become ten.
Two pink doves strut the shingles
picking crumbs from the breakfast I saved
for you dear. And I wish you were here
on this postcard day.

Focus on the fine indeterminate line
where the sky meets the sea.
Desperate midweek words, banal and absurd
freely flow out of me.
Oh, I may be a hostage to summer
but I'm a hostage, not a slave.
And I'm clear that I wish you were here
on this postcard day.

Precious cargo of flotsam: mixed memories on an ocean tide
swim madly with spice from the orient
on a mystery watery carpet ride.
But with the sun going down, the wind goes around;
blows them back out of mind.

My eyes are wide circles staring down past the point
of my restless pen.
While the ghosts of my youth all sworn to the truth,
call my name again.
Two brown legs don't make a summer.
But two brown arms couldn't keep me away.
Well, my dear, I wish you were here
on this postcard day.

,-)