Without wanting to sound Biased
The Slow down came when Mitel Purchased ShoreTel, and it is across the board with regard to their Web interfaces SSO to MiAccess is much slower than the ShoreTel Equivalent, although I guess there are many more people using it.
In Australia ShoreTel / Mitel is sold as a cloud solution by Telstra (The National Carrier) and you are restricted to who you get your lines from currently, and I would say the take up is starting to speed up as the roll out of the National Broadband nears completion (National Broadband is fibre to the premise and Node in some cases)