I strongly suggest going with minimalist themes, so even if you get very tired of it, the change is not going to be very noticeable to the regular visitors (I'm thinking a minimalist theme to another minimalist one). Then again... it depends on what kind of blog/site you have. If say is personal blog, it's not a big deal to change themes even weekly (look at tumblr bloggers for example). If however your site/blog is a well-to-modest established brand, be it online of offline, then it's absolutely not a good thing to do.
thanks alot for the ideas..... what if i just change the color once in every few months? n keep the same layout? will it still bother my frequent readers?
It comes down to personal taste, and sometimes with a WP update if the theme breaks or if it's been customized. Primarily it's communicating with your visitors and regulars that it's still the same site - but with a face lift.
in my opinion if you change them often, people might get confused.. i guess changing the theme and stuff once or twice a year is enough..
l do not think it good for you to change your blog frequtently! your friends will find your are not so persisitant. and once a person chose his the best blog style,he or she would keep it for good!because it stands for certain charms !