Don't tinker with the status bar.  I don't want scrolling text, obfuscation of web and e-mail addresses, overwriting standard browser messages, and so on.  Leave the damn thing alone.

Code to standards and stop building browser-specific sites.  It amazes me how many I run across that work differently in each of the many browsers I use.  It's very annoying to have to switch browsers just to get a site to work properly.  Subsequently, test your site in more than one browser before you call it ready.  You're just being stupid.

Stop launching separate windows that are improperly sized.  If you're not launching a separate window for content that is always the same size on every screen and at every resolution (photographs, for instance, can always be measured in px), use consistent relative sizing or don't even think about modifying it.

Stop disabling the right-click context menu.  I don't want to save your stupid pictures.  Hell, I'm embarrassed you even posted them.  What you obviously didn't notice, in your haste to protect information no one wants to steal, is that there is other functionality you're taking away from me — like being able to open a link in a new tab or e-mail the current page address to someone.  Besides, disabling that function accomplishes nothing.  Ever heard of web cache, screen capture, page saving, and so on?  Duh.

Test your site using more than a few screen resolutions and color depths.  Not everyone has the latest and greatest.  800×600 is the minimum resolution you should code for.  Remember, though, that many run at resolutions well above that (like me).  This leads me to…

Size your pages by percentage and your fonts by em.  This ensures your site is scalable by using relative units of measurement rather than fixed ones.  Doing otherwise wastes screen real estate in many cases and disables the user's ability to change font sizes based on preference/ability to read.

Code for accessibility.  Not everyone who visits your page is actually viewing it in a browser; many access it via a reader (which vocalizes content for the visually impaired).  If you don't code appropriately, you render your site difficult or impossible to navigate and utilize for those folks.  If you want to test your site's accessibility rating (Section 508 compliance), go here.  Show some consideration for those not as fortunate as you, even if it's only by making your site compatible with the software they need in order to visit you.

Put target="_blank" support into the next version of XHTML strict.  I always want to launch external links (those to other sites) in a separate window so it's simple for visitors to return to my site (otherwise, checking any reference in a post would lead you away from the site; that's a bad viewer-retention practice).  Having this functionality removed from XHTML strict compliance means I'll never get away from transitional.  It's annoying.  And what logic was involved in determining it should be removed in the first place?  Oh, I see.  None at all.

[don't make me have to tell any of you again]