Changed my keyboard layout to Colemak cold turkey as it were a month ago and it seems I've hit a plateau at around 52 WPM (no improvement for a week) compared to the 65 WPM I peaked on QWERTY and I'm a lot slower when free typing like I am now.
The main site I use to practice on is http://keybr.com/ and also the program Amphitype.
It's most frustrating when I want to type in something quickly into a chat box or do a Google search, because I have to get my fingers ready on the home row and get into the touch typing mindset even if it's to type a couple of words and that's very slow.
I also have doubts about whether Colemak is better for the average human. Yes all the common letters are on the home row but in a way that's reason why it's so hard to get faster, there is a tradeoff. On QWERTY you are forced to move your fingers all over the keyboard so the brain is exercised more and makes more neural connections which is easier for the muscle memory. Anyone who knows anything about memory will tell you this; the more pathways that link to a memory the easier it is to retrieve that information.
Paradoxically some of the words I find hard to type are the words with most of the letters on the home row. "Disordered", "received", "returned", "retrieve", there are also words that I type very fast so there seem to be many hot and cold spots in Colemak typing, more so than QWERTY like someone mentioned in another post. The hot spots don't make up for the cold spots. A car traveling at 60mph for 50 miles then 40mph for 50 miles will not reach its destination as quickly as a car traveling at 50mph for 100 miles.
Another reason I'm not getting faster could be psychological. The very thought that I may go back to QWERTY makes me cling on it somewhere in the back of my head so I can't shake it completely especially when I want to type a couple of words fast.