While I've been a member of the OmniFocus "Sneaky Peek" for some time now I hadn't really embraced it yet. This is a result of the fact that things have been very busy lately and I've got such a smooth workflow with iGTD that I, frankly, wasn't all that motivated. I then began a series of email correspondence with Robin Trew, who is, by they way, much smarter than I. Rob put together an amazing apple script that yanked about 250 tasks out of iGTD and dropped them into OmniFocus in as much time as it took me to brew and consume a cup of green tea.
Rob having saved me the tedium of transferring data, I began playing in earnest with OmniFocus a few days ago and it looks like I'm not going back to iGTD. I'm not taking anything away from iGTD which is a very good application (and free!). Indeed, with Quicksilver triggers and other features I think iGTD is, in several ways, superior to the current OmniFocus alpha I'm working on. However, after a few days usage I can already see the writing on the wall. Frankly I'm willing to have a little less efficient input in exchange for other benefits in OmniFocus. Specifically, I find the ease of use in moving and copying task groups, the better data management, the ease of use in designating projects with concurrent or subsequent tasks and the general fit and finish of the program have me hooked. Rob also explained the data security in OmniFocus is better. Being that I was an arts major and I still leave cheese out at nights just in case there IS a little mouse inside my Mac on a wheel, I'm simply going to paste Rob's explanation here.
"The iGTD approach of storing everything in a single binary (SQLite) file does introduce a slight vulnerability - a binary file can be quite hard to retrieve things from if it gets corrupted. Omnifocus also uses SQL internally, but it stores everything on disk as a cloud of (gzipped) XML files - one for each transaction, which is inherently rather robust. (Regular backups are streamed out as single XML files, which, like the small transaction files, become human-readable as soon as you gunzip them in the Terminal).
There is a more lucid and authoritative account here."
So it looks like I'll be talking more about OmniFocus and less about iGTD. Unless, of course, OmniFocus is not up to the task and then you will hear all the gory details right here. For those iGTD faithful I say stick with it. If it weren't for OmniFocus, I certainly would. I don't think questions as to which tool you use to accomplish your productivity is really, at the end of the day, all that important. The question is whether you actually are productive.