For one of our clients, I've been working on converting printed forms into web forms, and in the process have been dealing with a lot of tables that need to fit within a fixed width.  These tables are in a FormView in a User Control, which are then placed on webpages as needed.  I was finding that Visual Studio 2008's design mode was happy enough to accept my fixed-width columns and tables settings in my CSS stylesheet when working on the User Control, but once that User Control is placed on an actual page the fixed-width settings are no longer respected in both design mode and in debug mode displayed through a browser.  What to do?  After much frustration I found the embarrasingly simple answer: I wasn't putting "px" at the end of pixel measurements for table/column widths.  For whatever reason the Visual Studio 2008 FormView designer was content without the "px" but nothing else was.  In my rush to get things working I was leaving off the "px" figuring that I could go back later and add them on after the fact.  So lesson learned: be standards compliant, even if your development tool of choice lets you get away with not being standards compliant.

Still on the topic of fixed-width tables and columns, have you ever wanted to figure out exactly how many pixels wide/tall something is on a webpage, be it a table row, table column, header graphic, etc.?  Enter Pixel Ruler--a free app that displays a rotatable ruler on your screen and even tracks your mouse cursor and keeps a running measurement of how many pixels away you are from the zero mark on the ruler (in one dimension of course--it doesn't do diagonal measurements).  This app will save me countless hours of eyeballing and hoping for the best, instead providing me with precise measurements to the pixel.