As usual, the installer includes a Spigot-based YTD Video Toolbar and offers to change your default search engine to Yahoo and add 5-6 shopping extensions to Google Chrome. Clicking the "Decline" button during the lone advertising screen in the installer lets users easily opt-out of all offers.
Always opt for custom install on anything you install and read everything 3 times before clicking next.
Another good ipad app is Video Downloader Lite. Its free but with the lite version you can only store up to 10 videos. Just browse Youtube through the app and click on the movie, you then get an option to download. The paid for version £2.99 I think does away with the storage limit and removes the ads etc.
All sound advice above. Personally I prefer "Download helper" extension for firefox. It allows you simply download any video [youtube included] onto your PC. The operation is simple as whenever there is a video in any active window, the extension symbol on the firefox menu starts spinning automatically and click on it to download.