1. They set SPF policies of "-all" on customer domains. These customers have no idea about SPF and often use 3rd party software to send account statements that never get delivered. This breaks email for their customers and for everyone else. They should set "~all" by default as Google Apps does.
2. They claim not to, but they definitely block entire IP ranges rather than a single IP address. A noisy neighbour in the same datacenter as you can get you blacklisted. Use http://www.senderbase.org/lookup/ip to monitor your neighbours and report them to your hosting company. If you spot a bad neighbour, you will no doubt see your own IP blacklisted at Outlook.com's https://postmaster.live.com/snds/ipStatus.aspx within a few hours.
3. They are well known for accepting mail and then silently dropping it, without bouncing sender or receiver and without putting it into a spam folder, even when the sender is a longtime sender to that receiver and when the sender is sending personal anticipated email. They should either reject at the SMTP transaction (sending a bounce later is bad practice and leads to backscatter) or else deliver to a spam folder. Silently dropping email breaks email for everyone.
The sad thing is that many businesses are switching to Office 365 and Outlook.com.