Oops. I thought you could copy and paste IPA characters within the
same post but it apparently didn't work. In case Urban wants a
readable reply, I'm latinizing the Lithuanian and Cyrillic
characters :)

>In Vytautas Ambrazas' Lithuanian Grammar it says "[U]nstressed
>[long] vowels in Standard Lithuanian show a tendency to be shortened
>and turn into half-long (sometimes even relatively short) tense
>vowels. These changes do not harm the phonological system: the
>contrast is not lost, but only modified.

This is of course correct but in everyday "city" language the
contrast is actually lost: vyroo and vyru are exact
homophones. Mr Ambrazas and other Lithuanian philologists articulate
very clearly and urge everyone to do this, however, the real life
corrects phonetics in its own way. Yet if the loss of contrast leads
to any kind of dangerous ambiguity, both syllables are stressed in
vyroo, thus making it possible to pronounce the last vowel as
a long one.

>How close to standard Lithuanian [ae] would you say that this vowel
>is (as regards the quality of the syllabic nucleus)? And in what way
>(s) does it differ?

From the practical point of view, the long "e" in "Petras" is quite
different from "ja" in [pjat'] because a kind of "j" sound
(the "y" in "yacht") can be barely heard in the beginning of the
"ja".
This may be hardly spottable in Russian itself but when a Russian
says "Petras" he instinctively substitutes "ja" for "e" and
"Pyatras" comes out (analogously, a Lithuanian instinctively
pronounces [pjat'] as [pe:t']).

Juozas Rimas