I haven't been using Krita for very long, but I've already made it my sole painting software. Yup, I use nothing but Krita to create my digital art. I love the software. The brush engine is just amazing, and its quite easy to learn. However, it seems like it could do with a performance boost though (Lags a lot on lower end computers). Posting images on the forum seems a bit confusing for me, haven't used forums a lot so I haven't really come across such. Other than those, no complaints. This is an awesome software.

Depending on the OS and the computer used, experiment with turning opengl on or off, texture buffering on/off, the scaling mode; if the computer is really low-end, image resolution might need to be smaller and channel depth limited to 8 bits. For some Windows systems, changing the brush spacing can help a lot. And we don't worry about shipping some really complex brushes; those are brushes that do a lot of procedural work, and that needs a good CPU, there's no way around it.

In the end, I use Krita myself on the lowest-spec Surface Pro 3, and I don't get more lag on that device than with Photoshop, when using images limited to about 5000x5000 pixels.

On the other hand, we are working on improving performance when working with bigger images and bigger brushes, but that's stil experimental.