I wish Visual Studio had Multilingual User Interface (MUI) implemented as on Windows Vista
When developing commercial add-ins for Visual Studio, chances are that you will have to test it with international versions of Visual Studio to ensure that your tool works fine, say, in Visual Studio Spanish or German or French or Japanese or Chinese or whatever. While Visual Studio .NET has always supported multilingual interface (via "Tools", "Options" window, "Environment", "International Settings" section, "Language" combobox), this requires you to install the whole localized version of VS on top of the existing (English) one to have another language in that combobox. And here it comes my complaint: you can almost watch an entire movie while Visual Studio is installed, and lately even when a VS service pack is installed (I had time yesterday to go to run to the park and get the shower before VS 2008 SP1 got installed), so you can spend a whole day installing all those languages.
Windows Vista offers an elegant solution: the core of the product is language-neutral and language-packs are provided for the UI. Supposedly the core + language packs are much more small and manageable than the multiple localized versions. I wish Visual Studio used the same architecture. It would even fit in a single DVD for distribution purposes and the setup would prompt you which language(s) to install.