A trend Google has been pioneering in many Cloud applications is a sort of "autosave everywhere," especially noticable in Google documents's immediate save feature. I personally greatly prefer this functionality but it seems some situations clearly don't call for it; for example anything that might affect live data.
What affects whether a user should be in control of the save operation? So far I've considered:
Privacy/Security: Personal information like real names or information subject to attack like Credit Card numbers should only be submitted with her's explicit consent.
Ability to review: Gmail's draft feature is a good example of this; whatever you do is saved but nothing "real" happens until you hit the send button. I feel this could be applied to forms but the option seems a bit murkier there.
Discrete, reversible steps: If autosaved information may overwrite information it should be reversible. Google Docs addresses this by having a reversible "history" of edits, but makes the history fairly hard to use. Edits aren't grouped well so 10 minutes of editing might show up as 100 explicit steps to reverse. It's similar to Wikipedia's revision history feature, but that doesn't autosave.
Awareness: The most painfully annoying aspect I've encountered is when I don't know whether something has saved. Whether you want something to save and it doesn't or you don't expect something to save and it does, you're going to be mad.
What other considerations are there? What haven't I considered in the above list?