APS-C and smaller sensors seem to have plateaued off in terms of their megapixel counts, possibly due to diffraction limits. The ISO performance of these sensors has not increased substantially in the last 2-3 years. APS-C seems have a usable peak ISO of 3200, and this is lower for smaller sensors. It could be just that my expected technology upgrade speed is unrealistic, but things seem to have slowed down somewhat in the last year or so.
Canon for example has not significantly upgraded their 18 MP APS-C sensor that debuted on the 7D in 2009. Most of their upgrades have been on the supporting CPU (Digic 4\5), ergonomics (swivel screen), mechanics and user experience (touchscreen). Prior to this, they had a 1-2 year upgrade cycle for their sensors. This chart on wikipedia gives a reasonable list of the mainstream DSLRs and their specs.
HTC for example is trying to reverse the megapixels race by going for larger pixels on the HTC One, while Nokia is also sticking to around 8 MP sensors for the time being (PureView 808 aside). Apple (iPhone 4S & 5) and Samsung's (Galaxy S II & III) entries in 2011 & 2012 also had similar 8 MP sensors, whith improvements coming from the remaining hardware and software.
HTC's approach is probably a bit extreme as the 4 MP sensor sacrifices a bit of resolution in well lit scenarios, going by its reviews. 13 MP seems to be the upper limit for camera phones, while 8 MP might be the sweet spot.
Point & Shoot
Point & Shoot cameras have also peaked around the 16 MP mark, and back illuminated sensors were one of the approaches to improve low light performance.
TL;DR: Are we nearing the point where the sensors have neared their optical limits and most of the improvements in image quality will be from the other components? There are definitely improvements to be made on dynamic range and ISO improvements\low light performance, but are those changes happening at the same rate? Are these low hanging fruits or will they take more time to get addressed?
Update: Found a very useful comparison of the iPhone camera across generations, right from the original iPhone to the iPhone 5.