Gmail search has gotten a small but very important improvement, it can now search inside attachments even if they aren't plain text files. For example, you can now search inside PDF documents attached to a message, making the search feature a lot more useful.
The new feature
also works with other type of documents, Word files, PowerPoint presentations and so on, basically everything that's supported by the Google Docs viewer.
It's likely that this is where the technology comes from in which case the only question is why it took so long. Google even enables users to search through scanned documents or images courtesy of its OCR technology.
Still, the new search capabilities are now finally available in Gmail search, so finding the attachments you need, even if you don't know exactly where they are, should be a lot easier.