Maybe a subjective question, but is Msmq reliable compared to JMS solutions?
There are no reliability issues with MSMQ unless you are have to many different machines connecting to one MSMQ service. We maxed out at 2-3 servers sending to a queue instance and 2-3 servers reading from a queue instance. Keep in mind that we send millions of messages per minute through the queues.
Udi Dahan, of NServiceBus, has written about using NServiceBus backed by MSMQ on his blog here. The discussion is more about performance than reliability, but you should find it an interesting read.
Here is someone running 500 messages a second through NServiceBus (again backed by MSMQ) without any issues.
I've only used MSMQ for applications with much lighter loads, but I've never experienced any reliability issues.
In addition: it is as realiable as you make it. Depending on configuration you may loose all messges on a server restart. This is a configuration choice, though (faster, queue only in memory).