There are two major issues that crop up in my experience.
* Node as a runtime is deeply mediocre, in my experience. You can usually solve this by throwing more (usually virtualized) hardware at the problem.
* Meteor's architecture is (at present) tied into MongoDB's oplog tailing. You can scale it up through sharding, through alternate libraries, and DDP itself is not tied to MongoDB at all. IIRC fixing this was a goal for Meteor 2.0.
Both of these can be worked around. If nothing else, the Meteor web side will talk to anything doing DDP, and DDP is not that hard to deal with.
* Node as a runtime is deeply mediocre, in my experience. You can usually solve this by throwing more (usually virtualized) hardware at the problem.
* Meteor's architecture is (at present) tied into MongoDB's oplog tailing. You can scale it up through sharding, through alternate libraries, and DDP itself is not tied to MongoDB at all. IIRC fixing this was a goal for Meteor 2.0.
Both of these can be worked around. If nothing else, the Meteor web side will talk to anything doing DDP, and DDP is not that hard to deal with.