I'm currently working on a public MOSS Publishing site. As is normal on such projects, code is being cut on Virtual Machines on the developer PCs, and later placed in an integration environment to make sure it works. A couple of errors arose recently during the integration of web parts which I think are worthy of note.

 First, a web part is added to a page layout. The page refuses to render with the error "Compiler Error CS0117 'Type' does not contain a definition for 'Identifier' ". This was most confusing as it works fine on the dev machine and well frankly the error message doesn't give a good hint. Eventually I googled this; http://msdn.microsoft.com/en-us/library/c4aad8at(vs.80).aspx

In the mad rush to develop the web parts, the developer had kept the default namespace and class name in the project. These were the same, and that was causing this error in Integration (but not dev). Following the good practise of changing the namspaces to a standard one for the functional area (and no longer being the same as the class name) fixed this issue.

 Second issue of note. One web part renders a Link button. As you probably know this uses javascript to action the postback. Clicking on the Link button in Integration gives the javascript error message "'null' is null or not an object". I didn't find any specific article that nailed this one, but I saw enough to give me a hunch it was a validation control issue. For some reason, the required field validator rendered by another web part on the page seemed to cause this error. Removing that validator fixed the issue. Luckily the validator was overkill and could be removed. In the mad rush of projects we didn't check all the options. It could be that turning off the validators client side javascript property would've done it, but hey what can I do? Our release date looms large!  ;)