Sometimes, we see the nice new shinny theme with all the bells and whistles that we must get. Not often until after we unwrap the packaging and install it that we encounter a few hiccups.
Most WordPress themes in particular are designed for sidebar widgets that are good for later WordPress versions, not versions that are 2.0 or sooner.
When one tries to preview the blog in a browser, there are often PHP error notices that either yourself (if you are versed in HTML/PHP) or a WordPress Pro would have to de-bug in order for you to use your new theme and/or template.
So before updating that theme, it important to ask yourself is having the “theme of the moment” critical to your business, or are you just having fun with the shinny new toy.