FYI: I ran a Drupal patch (http://2bits.com/articles/measuring-memory-consumption-by-drupal-bootstr...) that ranks modules by memory use, on a site I'm working on that is suffering from having too big of a memory footprint. Here are the top results on the front page, which does not use anything from ubercart directly:

Start,61672
End,47397932
Total,47336260
uc_order,1802728
uc_store,1221108
user,1115516
uc_cart,1067692
node,1020940
uc_product,870952
system,855588
views_ui,813980
nodequeue,635556
comment,597660
views,567336

It'd be nice if ubercart could reduce the memory footprint of uc_order and uc_store especially.