Works fine for me across the board. My only issue with it is how it's eating ~2gbs of disk space on my phone for attachments. I haven't figured out a way to get rid of it without going through and purging all my messages or formatting my phone.
The only odd behavior I get is that, occasionally, the desktop client will take a moment to catch up to the other devices, or be missing chunks of a conversation. That usually sorts itself out in under two minutes or so, though, so I assume it has to do with the time it takes iCloud to respond.
EDIT: I'm still on 10.8, if that's relevant. I intentionally lag a point version behind because of audio software (the latest and greatest always breaks audio).
Occasionally there is a hiccup where a conversation thread is not immediately synced with the other devices, but that seems to be happening less and less.
If I use Messages just on my iPhone, it works just fine. However, when I use it between 2 macs, an iPhone, and an iPad, it just breaks.
Sure, it's an edge case use - most people use messages just on their phone - but it's a pretty basic feature.