I keep seeing the same question on a lot of the social media sites so I want to write a blog post covering everything.
When we released Plasma 5.0 we had gone through a lot of large technical changes throughout the stack. It was expected that there are some regressions, either from bugs or simply some minor components not being priorities as being needed in the first release.
There is no such thing as a "normal" user. Everyone is different and what is rock solid 100% stable to one person may be very problematic for another. This makes it very hard to give a single answer.
A good example of this was translations. Due to some changes in frameworks when we released Plasma 5.0, we made a very poor job of translation loading and a sizeable amount didn't work properly. Most developers tend to run things in English even when they're across the world and it simply fell through the cracks till it was too late (fixed for 5.1).
If you're a user who uses KDE in English, this naturally isn't a problem that would affect you. If you only speak German this would be a complete showstopper that would make you absolutely hate the 5.0 release.
This same philosophy applies screen hotplugging or specific graphics hardware or RTL layouts. It might be a massive problem, you might find everything works perfectly.
To determine if Plasma 5.1 is "ready for you" the only real option is to try it.
It might seem like it would be a good idea to keep the project in beta until there are no regressions but under open development it simply doesn't work.
We don't get the level of developer and user interest we need to catch and fix all regressions without a release. There's a common mantra "release early, release often" for a reason.
It's also worth remembering that whilst we have some regressions, we also fix a lot of things and it's important that users can chose to reap those benefits.
Everyone is being very conservative with our 5.x release mostly due to historical reasons of other major releases; Kubuntu in a few weeks will release two ISOs one with classic KDE SC 4, and the other with Plasma 5.
I've seen a few people suggesting that they can't upgrade as there aren't any applications released on Frameworks 5 yet.
We have put a lot of effort into making sure Qt4 applications fit in natively with Plamsa 5. We make sure system setting syncs as many changes as possible and we have even backported the latest theme so that applications fit in natively. It's near impossible to tell the two apart.
The original plan has always been that we will release applications slowly after the workspace is ported.
Trying to remove Qt4 applications immediately is not the plan, nor is it encouraged by us.
Personally I've been using Plasma 5 in development for 9 months, and I am so accustomed to any remaining issues that I massively prefer it over what we had in 4.x.
From 5.1 I would be comfortable recommending upgrading to users who use KDE casually at home.
If you want Plasma to be better as soon as possible remember to join us in #plasma on freenode and contribute.
Also we are starting our year end fundraiser more sprints will result in more fixes, faster.