Update (10/14): It looks as if this hack was originally developed by Sharath (explanation provided at the bottom). See his post for an updated version.
Although there are plenty of hacks out there that make it easier to format text in ones scrapbook or forum (such as the Orkut Toolbar), this one by far seems to most useful.
Created by Siva Jawaji, the Orkut Formatting Toolbar provides easy to use formating buttons above not only the "general" scrapbook box...
...but in the reply boxes as well.
You can even use this hack while replying to various forums on Orkut.
Currently users have to either remember 30 different formating codes ranging from smilies to colors to the basic [b]bold[/b], [u]underline[/u] and [i]italic[/i] codes (either that or constantly refer back to the Orkut chart).
Siva's hack removes that hassle, making it easier for even non-geeks to concentrate more on what they say, than the appearance of the message on Orkut.
Hopefully Google includes a similar feature later on this month, when they open up Orkut with API's.
Note: This hack is for Firefox users (sorry IE fans). In order to use this hack, you will need to first install GreaseMonkey. After that, you can download Orkut Formatting Toolbar over here.
I will add this hack to the Orkut User Tools sidebar underneath the GreaseMonkey section.
Update (10/14): It seems as if their is a dispute on who is the original author of this hack.
Siva's hack (featured above) seems to be based upon a previous script by MarivaldO.
However Sharath is claiming that both scripts are based off his original hack, which he has improved upon by adding glitter effects (which looks really nice by the way).
I (hopefully) doubt anyone purposely took this hack for their own, as they could have simply forgotten to credit the original creator.
Since it looks as if Sharath may have been the original author of this hack (at least to me), I'll give him credit for the original hack.