iOS 6.1.3 caused both a dramatic battery drainage on my iPhone4 + connectivity issues (text message, phone call issues).
Personally a great fan of iGadgets with the house & pockets loaded with iPods, iPads, iPhones, AppleTVs etc. As a self-observation, however, I've now reached a tipping point where my personal comms usability & reliability requirements force me to seek for another, hopefully better suited device. Perfectly aware that the battery drain & connectivity effect may not be universal, may not appear in all environments & some tweeks here & there might improve the situation a bit, but doesn't really make a difference - I need my phone & messaging to work.
Have now twice faced the battery drainage problem over the past few years (step change with an iOS update that makes the device useless). The first one was eventually fixed with an iOS update, but for the second time I'm not willing to wait nor to read through threads with minor optimization hints when the problem is fundamental. The simultaneous connectivity issues after iOS 6.1.3 have now almost cost me a fortune with critical calls & text messages failing to go through.
So continue to love the gadgets for many other purposes but personally this is the time to check if other smartphones can better meet my requirements for reliable comms. Hope the bug gets fixed & the iX:s get back their battery span needed for my other use cases.