I don mean to pick on any fellow cser. following is just my own personaly opinion. i think watever camera doesn't really matter loh... most important u must be happy with ur set of equipment and u must b happy with ur photos.... not every photo taken by famous photographer using top notch equipment are well liked by every single individual. while we always read comments on how nice a pix from those that used pns too.
as for y upgrade from 40D to 50D, well depends on individual user defination of 'worth or not' loh. in Jan 1st '07, i started with 400d in Oct '07 i switched to 40D and i was very happy with the extra features and 14bit processor. now i just upgraded to 50D and i find the change worth. i simply like the 50D's LCD, on 400 and 40D e LCD not so accurate, with e 50D its very sharp and i am more confident on the output now. i mainly take photos of my kids hence, to me immediate accurate feedback is more important cos once missed i will not get the same pix anymore.
lastly, hee.... i'm not surprise that i may switch to 5DMkII when it comes... meanwhile i am happy with the 1.6crop as it mainly capitalizes the best of EF lens. BTW i don own any EF-s.