I've got the same problem. Photos taken on my iPhone and iPad all used to appear virtually immediately on my laptop Photo Stream (so long as phone/ipad were connected to wifi) . Since updating to ios8 ... nothing. It's really annoying because I take loads of photos for work, and it was so easy to be able to upload them direct from the PhotoStream, now I either have to connect iPhone by USB or email them to myself.
I must say, I've never found PhotoStream the most reliable thing ever, it did used to stop working every couple of months, but nothing that logging out of my iCloud control panel and back in didn't solve. However I've done this numerous times and even resorted to removing and reinstalling it, nothing works and I really don't know what else I can do. Photos I take on iPhone appear on the "Recently added" photos on iPad and vice versa, but nothing on the laptop.
I did hear a "rumour" that Apple are going to reinstate the good old Camera Roll and PhotoSteam on the next update, due October 20th ... hoping this will alleviate the problem otherwise I guess I'll have to start using DropBox.