One member said they update every hour and lag about 3 hours behind in reporting:
mine updates about every hour, and is almost always exactly 3-hours behind.
Others suggest it is more like every few hours.
But if you take a look at the Google Analytics help center, which says:
How often is the data in the reports updated?
Report data is generally updated every 24 hours, but data may sometimes take longer to appear in your account. AdWords cost information is imported once daily, to import the previous day's information.
So who to believe?
It seems like I saw an early update this weekend, but I was not a 100% sure. 24 hour updates make most sense to me. Here is a poll where you can add your two cents:
Forum discussion at DigitalPoint Forums.