It does take up massive amount of memory. That is one reason I was considering PPC Tech's 128MB RAM upgrade. SPB MS 3 does respond faster than 2, you should have seen 2's sluggishness

.
IMHO, the intuitiveness of allowing gadget customization far excels Windows Mobile's default crappy layout (Which was just ported from PC) and iPhone's tile layout.
Another PPC shell is
Touch Commander. Never tried it, so no opinions from me.