I just sent in the below feature request, exactly along these lines. It would help me a lot!
(I hadn't thought of the suggestion somewhere up-thread to use a calendar event to trigger the monthly creation of the OmniFocus task, thus allowing me to mess with the start date however each month. For this route to work for me it definitely has to be automated, which would be simple with applescript. Seems like an excellent suggestion, but I will have to think about whether the extra complexity is worth it to me, particularly in that it puts an additional potential failure point in the process of making sure repeating events get in front of me at the right time. But, it might be worth it. If I go that route I'm much more likely to go with a launchd item as I already run a ton of custom timed scripts through there for other tasks.)
I really like the feature of "Repeat Every" and choosing a weekday. The killer aspect of it for me is e.g.: I can set something to repeat every Thursday with a due date of Sunday and then during the actual week I can push the start date of the event back without messing up future occurrences. (e.g. at my house I need to run the septic pump for 10-15 minutes some time each week before Sunday night to avoid having the alarm go off in the middle of the night when the water filter flushes - don't ask why… Because I'm sometimes out of town on the weekends I set the event to repeat every thursday with a due date of sunday evening. If I'm going to be in town I can delay the start date until the weekend when it's more convenient without screwing up the timing of the repeating event the following week.)
Feature request: It would be incredibly useful to me to extend this "Repeat every" functionality to:
- day of month (e.g. "Repeat every 23rd of the month", and it would be great to also include "Repeat every 2nd Tuesday". But, just the "Nth of the month" would be huge for me.)
- day/month of the year (e.g. "Repeat every June 1st")
The above features would be very useful to me for bill paying and a variety of other tasks. e.g. have "Pay Bank X's credit card bill" repeat every Nth of the month when it comes available, but allowing me to push the start date as appropriate each month to hide it from myself until I'm going to pay it. Similarly for some annual tasks that come available on one date and may not be due for 3 months. I want them to be repeating and come available on that same date next year, but they are also not a high priority to take care of immediately at the start of their 3 month window.