The Google Toolbar has an AutoFill feature that automatically highlights form fields like name, email address, and phone number, and fills them in with the click of a button.  It's an extremely useful feature, and it's one of the major reasons why I use the toolbar.  However, it occasionally causes some problems.  One problem I was having on my site was that the search box was being highlighted yellow because the toolbar thought it was a fillable form.  I found a few attempts at a workaround but didn't find any I liked.  But this one gave me an idea:  Add an onload event to the body tag that changes the background color of the input field to nothing.  For me, it looks like this: 

<body onload="document.searchform.searchinput.style.backgroundColor = '';">

And it works perfectly.  Ahh, a solution to a problem.  [Edit:  Maybe not; see below]

Another problem happens with a bunch of WordPress themes.  For whatever reason, theme designers sometimes put labels after their corresponding inputs, so Google Toolbar sees "Name" and then fills in the following input, which is for email. 
A workaround to this is to put labels chronologically before their corresponding input fields, and also to use proper labels.  For example, don't use "Mail" when you mean "Email".  Also, use label text sparingly.  Put warnings and restrictions after the input field.  For example, use "Mail" instead of "Mail (will not be published)".  Put the "(will not be published)" part after the text box. 

Update (2007-01-31 3:43pm):  This seems to work some of the time, but not all the time.  I noticed that when I navigated to a different tab in Firefox and then back to the tab with my site, the search input box was highlighted again.  I give up. #technology