The EOL guide should shed some light into the release cycle.
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In addition to Pattabhi's reply here are some notes from experience.
As a rule of thumb one can assume that major releases will be published every 12-24 months.
Beware that the term "major release" does not necessarily mean an increase in the first version number. For example, PowerCenter 8.0 / 8.1.x and 8.5.x/8.6.x were more or less considered different major versions; 8.0 was released in 2006 and 8.5. was released in 2008 (if I recall correctly).
Bug fixes are released on an "as needed" basis.
A "hot fix" is a roll-up of all bug fixes since the last minor version or hot fix. Sometimes (not always) such a new hotfix version also contains new functionality. Whether that's the case or not depends on too many factors to give any rule of thumb here; read the release notes of the respective hot fix version, then you will learn whether new functionality has been introduced.
Informatica recommends to install hot fix versions as soon as possible after they have been published; as mentioned earlier, each hot fix contains all bug fixes published since the previous hot fix (or minor version, if this is the first hot fix), so you can pretty safely assume that the new hot fix is more stable than the previous version.
Again, these are rules of thumb from previous experience. These are by no means any "official" statements, just my experience.