Apple's products are in much demand these days. They have products ranging from small desktop computers (the Mini) to notebooks (MacBook and MacBook Pro) to desktop computers (iMac and Mac Pro). In addition, they carry many different lines of iPods, iPhones, and iPads.
However, unlike most tech companies, Apple seems to update their line of computers on a fairly infrequent basis. That, coupled with their lack of information regarding future updates, makes it very difficult to know when to buy a Mac. After all, you would want to buy the product as soon as the product is updated as this is when the product has the most "bang-for-the-buck."
There are some little things you can do to make a more informed decision before you buy. Here are some tips.
First, figure out what product you want to buy. This is the most obvious step but is very important as Apple usually does not update its entire product line at once. If you know what you want to buy, you will have an easier time with the following steps.
Next, find out when your product was last updated. Although Apple is generally very secretive about future updates, they do seem to follow a certain time pattern in releasing updates. Some websites have this information. If the end of the product life cycle is near, it may be wise to wait.
A good source is at MacRumors: http://buyersguide.macrumors.com/
Third, read rumor sites. This is somewhat risky though because there are many rumors and a lot of them end up being untrue. For instance, many rumor sites were predicting a redesigned iPhone 5 to be released in 2011. However, Apple instead released the iPhone 4S. Despite these mistakes, rumor sites have been known to occasionally get predictions correct. Therefore, reading them may give you an idea as to what may be expected in a future update.
Also, wait for big events. Apple holds the World Wide Developers Conference (WWDC) every June and frequently announces updates to its products then. Apple also holds press conferences at various times during the year to announce a new product or initiative.
And lastly, if you absolutely need a new computer, just buy one. Sometimes waiting isn't an option and can also be a little bit of a gamble as well as you never know if the updated product will live up to your expectations (from reading the rumors about exciting new changes). Remember all technology products become outdated in a matter of months and waiting for the newest model will not "future-proof" your investment. However, take comfort in knowing Apple products are very well built and should last you many years of solid use.