That depends on several factors. Really, first off, what do I do with an iWatch to begin with? Is it just my notifications and maybe Siri on my wrist? Does it add more functionality? Why do I want this thing?
If it does indeed give me some functionality that I feel warrants buying it, if it lasts 24 hours of normal use and I just have to charge it over night along with my phone I don't see why that would be a big deal. I charge all my other devices over night every night, and it causes me no pain or problems.
The big issue for me would be if it can't last through the work day and I find myself in the position of having to take it off and plug it in while working or it dying while I'm out doing something after work. If it's going to last the whole day and I just have to charge it at night no problem; if I have to top it off throughout the day then it's not worth the hassle.