I have used both hog and sheep casings on a number of occassions and really never seen what all the fuss was about re the delicate nature of sheep casings. Although I agree you do have to take a little more care with them, they are not as some people would have you believe made of gossmer.
However having just recieved a new batch of sheep casings and having tried to use them a few days ago, these are the problems I ran into:
1) Casings far too tight, so tight in fact one string would not fit over the thinnest nozzle of my reber 5k. Being too tight meant IF they fitted over the Reber than the next stop was to split.
2) Very thin strings running off the casings which sometimes meant when you tried to remove them they would split the casings.
In conclusion, had I not tried the sheep casings before this batch, I too would have been writing to denigrade them, but knowing what I know now I am aware it is just a bad batch. Therefore if you have suffered the aforementioned problems just give them another go, you may be surprised!