In Spezzafer's submission thread,
bullethead2202 posted two movies showing walljumps in Yoshi's Island. A walljump could for instance save time at the end of 2-1, where there is a small wait before a rock that's falling down is low enough to jump on.
NxCy and I don't have a consistent way of performing these walljumps, and bullethead2202 stated in a PM that it was more trial and error. On the (E) version, we can get walljumps quite easily by randomly trying, we haven't been able to do even a single one on the (U) ROM. Also, even on the (E) ROM we haven't been able to do a walljump on a moving wall/rock.
As it's only a result of randomly trying, we aren't 100% positive that it's not possible on the (U) ROM, or on moving walls... but considering the ease of doing them on the (E) ROM on stationary walls, we decided that we're sure enough that it's not possible to move on.
(One of our theories is that Yoshi's speed seems to be in the 900s in the (E) version, which is a bit higher than in the (U) version, this might also influence it... the (E) version also doesn't run nearly as stable as the (U) version it seems.)
Either way, if someone were able to do walljumps either on the (U) version, or moving rocks, it would be nice to let us know, otherwise we'll continue :).