The perfect lens? No. The perfect lens for me. Yes! I shoot primarily travel and this lens has it all for my needs. I guess I'm not like a lot of people here. I don't like carrying a lot of gear. I don't want to carry lots of gear. I travel light. I like to "blend-in" the best I can when traveling. I don't do tripods. I don't carry or aspire to have a bag of lens. I don't need or really want "L" glass especially given the cost and weight. What this lens has for me: Great range - I love the wide 17mm. Once you have it a lens starting at 24mm or 28mm will never do. IS which is perfect for low light and indoor situations - and really works especially combined with higher ISO if need be. So, goodbye tripod! UM for fast focusing. If this suits your needs go for it.
I found any CA and distortion on the wide end (which occurs on many lens - even "L") can be corrected using the amazing DxO software (http://www.dxo.com/en/photo/home/default.php) if it bothers you. This lens and my cheap 50/1.8 are all I carry and rarely miss a shot I want with my 350D Rebel XT. I'm not a pro but this set-up works for me. Pictures shot with this lens have appeared in major newspaper travel sections. So, it is passing muster with finicky photo editors.
After too much research I came to the realization that: 1) There is NO perfect lens. Zooms especially are all about compromises. 2) You will NEVER get any agreement about any lens on this or any other forum. Every lens gets praise and trashed. 3) Don't believe all the hype and hysteria about "bad copies." Are there any? Probably. But, 99% of the problems are due to bad photograhers NOT bad lens copies and 4) Get a lens - this or some other lens - that best suits your individual shooting style and needs and start shooting.