Personally, I haven't much used the PS2's backward compatibility for years, that doesn't mean it wasn't a much used feature when I bought it and some months afterwards.
I played the most of Final Fantasy IX (a PSOne game) on my new PS2, and a couple of other great PSOne games too, that were released after the PS2.
Nowadays, I wouldn't care much if my PS2 wasn't backwards compatible, but that's mostly because I sold almost all my PSOne games when PS2 launched, those few I left (Final Fantasies, WipeOuts, Ridge Racers) I have played briefly on my PS2, but as thetre are so many better games (and especially sequels of those old games) for PS2, I see little point in revisiting them other than for nostalgy's sake.
I would like to play FFIX again, but am hesitant because there just isn't time to put so much effort with all those newer games calling for attention.
This coming gen it looks much the same, FFXII is likely to be released very close to the PS3 launch, if not even after at least here in EU, also a couple of other must play titles are to be released so that I likely will have the PS3 to play them on.
BC is a great feature in the transition from old to new gen.
If MS is lagging with the updates on BC, maybe they are doing so in purpose. The old xbox hardly has any new releases scheduled, so they only need to worry abot the BC of old games, even if the compatibility isn't close to perfect, it's there anyway to be able to say xbox360 has that feature... they can just patch if tehere is user demand enough to make it worth it.
As it is (no new xbox AAA titles scheduled) I understand MS decision to not put too much resources on the feature.
It's there enough anyway to make it justifiable to be included in tech specs and marketing brochures, and there's always the possibility to patch according to demand, so it really was a sensible decision from MS.
Of course 100% would have been preferred, but sometimes being good enough is... well, good enough.