No, the "five device limit" is not at all "reasonable," especially when they broke the only way to remove a device and offer no clear path to resolution.
It's especially pathetic that the handset instructs you to solve the problem by using Zune, which has broken so the handset-recommended fix doesn't work.
They didn't even push out an update to Mango to eliminate references to Zune (which still wouldn't help in my case).
The ads say the smartphone beta test is over, but I feel very much like a beta-tester.
I shouldn't have to "send help tickets" and wait days, weeks or months for my phone to function properly.
I shouldn't have to search help databases only to see that the help articles on the issue refer to Zune before it was broken.
I shouldn't have to hope that someone at Microsoft's "online chat" will help me (during the limited times they're available).
I shouldn't have to sit and wonder what other part of the experience Microsoft will decide to break, without warning, next.
I shouldn't have to ask, when swapping out a phone (a very common occurrance) whether "this time" my phone will be rendered useless by an opaque Microsoft policy that cannot be changed... especially iinfuriating in the case of multiple broken devices.
I shouldn't have the fact that my phone doesn't work as advertised be dismissed as a "minority or uncommon problem" -- especially by a platform that cannot even hit 2% global share (and objects whenever someone describes the entire ecosystem as "minority or uncommon.")
That's why I left. User experience counts.