The way the updates have been coming out (since 1.3), I think it's probably the safest bet to wait until at least the .01 version comes out after a major milestone (i.e. 1.30, wait until 1.31--and actually a 1.32 came out). It seems like they always miss something and fix it in the .01 or .02 versions.
That's my personal philosophy, unless the major release has something that is too tempting to pass up. I'll likely upgrade to v.2--if that's what they call it--when the Euro launch of the PS3 happens. But I will keep a sharp eye out for 2.01 within the next few days after that