I think we all agree that the Weekly Review is key to doing a good job with GTD - of course, even Allen explicitly says it's perhaps the key to GTD.

Though it seems like drudgery, I love the fact that I have to toss my "next actions" index cards once a week (once they're filled with mostly-completed actions and I have no room for new actions) and copy the remaining items onto a fresh set of index cards.

It's the perfect time to do a Weekly Review because it requires thinking about each action as its recopied: "Do I still want to do this? Is this a project in disguise? Should this get moved to Someday/Maybe?"

This is one of the best reasons to go with a paper-based GTD implementation rather than a digital one in my opinion. I can confidently state that I'd have a tough time doing my Weekly Review if my next actions were in digital form.

This is true for any paper-based GTD implementation, of course - but it's particularly true for a hPDA implementation due to the small size of the index cards.

Disclaimer: This only applies if you're doing a full GTD implementation on an hPDA. If you're using a hPDA solely as your "mobile Inbox", it's less true. Although you'll have to process your Inbox more often, at least. :)