I've been using FacileThings for about a year and it's incredibly capable.
There are some negatives: The UI isn't as flash as some of the new apps and it's online only. However, it's implementation of the GTD workflow is unmatched by any other application I've tried.
It doesn't have a web clipper, but it integrates with Evernote, so that any notes added (or clipped) into the designated inbox notebook are surfaced in FacileThings for clarification. It can then add tags to the notes based on whether they are Next Action, Someday/Maybe, Waiting For etc. and optionally move the note to a specified folder. You can also apply tags that you use in FacileThings to the note in Evernote.
I also have it integrated with Braintoss, and use that for quick text, voice and camera capture. You can also capture by emailing to a custom FacileThings email address.
In GTD, projects (i.e., tasks which comprise of more than a single action) can have associated "Project Support Material". In FacileThings, projects can have an associated Evernote notebook, so that any notes in that notebook appear in the project as Reference Material.
It can also integrate with Google and Outlook calendars. I've got mine hooked up to my Outlook.com calendar, and items added to the calendar appear in the FacileThings calendar view almost instantly. It also works in the other direction, so if you get something in FacileThings (even notes from Evernote) it adds it to the Outlook calendar automatically.
So while it might not be the best looking app, or the cheapest, it's very powerful when used in the right way.