AJAX itself isn't difficult. Just get
JSMX, then it's a simple case of including a single JS file and writing a couple of functions per call.
Used it quite a bit for a thing at work and it's nice and painless.
Things can start getting more complex when you have to take into account the order of commands and so on, but that just means you have to think a little, and ensure you send/receive timestamps with your functions, and cater for timeouts. Code-wise it's still relatively easy.