my biggest disappointment wasn't in the lens, (Pentax 28-70 f/4) but the range. I'm glad I bought it used and for very cheap - since I didn't have money to buy the highly regarded Tamron 28-75 f/2.8. I almost bought it but I settled for the Pentax because I was low on cash.
I'm glad I went el-cheapo, because the wide end just isn't wide enough for me with the crop factor, and I hardly use it unless I have to. I'm thinking of the Sigma or Pentax 17-70 will work better for my shooting styles/subjects.
On another note, I have a total love-hate relationship with my 10-17 FE. Either I love the results or I feel like drop kicking it. I'm keeping it for sure, but it's cursed I tell you...