Commenter DaveHelps, on one of Paul Thurrott's posts:
I think Windows Phone as a whole is markedly superior to iOS and Android, and the improvements in 8.1, notably Cortana, are excellent. However: my experience of using a Lumia 520 running the dev preview of 8.1 as my main phone has been terrible, so I would think very carefully before choosing a 512MB phone for daily use.
Many apps take 3 attempts to load without crashing. Nokia Camera takes around 10 seconds to launch, if it launches at all. I have found myself manually closing apps several times a day but this does not appear to improve performance.
Can confirm. It takes me two minutes and several tries now, just to reply to someone on Skype. My phone didn't used to be nearly this slow.
The commenter goes on to suggest that this is because we're both using a developer preview OS, and the firmware hasn't been updated yet to support it. I am going to be much more careful about using and recommending "beta" quality software from now on, and am hoping that the Lumia Cyan firmware update will make my phone the awesome handheld computer it used to be.
In the meantime, please don't be surprised if it takes me awhile to respond or do stuff.