Job Application - how much can I/should I nag?

You can follow up persistently for quite a while without coming across as impatient if you always do it.  I think Mark recommended 13 weeks of follow-up before you give up (assuming they never respond during that 13 weeks).  Sounds like they are getting back to you, just not in a timely fashion, so you're nowhere near "too far" yet.  If you're interested in the job, what do you have to lose?
Just remember to be professional EVERY TIME.  Assuming the risk is that you lose the opportunity, consider what is most likely to hurt your chances.  Taking a laid-back approach may cost you the chance to even be considered -- you have to follow up.  Impatience may be seen as determination and persistence, so even if you feel slightly obnoxious doing it, there's relatively little risk.  But if you cross the line and become unprofessional even once, you probably lose the opportunity forever.
I was in a very similar situation last year, and I wanted to sound crisp when I left a follow-up voicemail, so I literally scripted out my message.  Then I made sure I was smiling (I'm the furthest thing from High I you can get, but I try to act as if I walked around the corner and was surprised to run into an old friend I was happy to see, etc.).  They can tell on the phone if you're smiling -- but since they can't see it, even more important to project some energy.
I just said something like "Hi xxxx, this is yyyy.  Just calling to let you know I'm still interested in position zzzz.  I know you're busy, and that's totally fine.  I would love to speak with you more about the job and how I might be a good fit.  I believe you already have my resume and application, but if you have any other questions please call me at 000-000-0000 or email me at [email protected].  Have a great day!"

I interviewed with a company 2 mos ago. Received several email telling me how interested they were in me..... 3 in total... always on a monday. I called and called and listened to excuses about corporate not getting back to them. Then one friday...The HR manager told me that I should look elsewhere and take another opportunity as they are going in a different direction at this time and tho they like me, I am just not needed. That was more than 3 weeks ago. Long story short, I started there today, after being out of work for 1.5 years!!! (expect miracles) I would be polite and call, but don't show desperation but rather appreciation for their time and efforts.
Please hang in there, I know how tuff it can be. You will work again.

To start - shift your thinking from "nagging" to I have a strategy for communicating professionally in my job search.
One of the most basic and helpful things I've learned from Manager Tools and Career Tools is that I get better at all of this stuff (managing, interviewing, writing thank you notes, everything) by doing it frequently and consistently - until it is "like breathing" (I don't have to think about it, I just do it). So if you are looking for a job, you should have a job search strategy for how you are going to contact and follow up with as many people and companies as possible, for as long as needed, in order to accomplish your goal of getting a  job. 
Rather than thinking about how often you can "nag" a recruiter about one job, approach it from the perspective of today one of my tasks is to send  a quick, brief note to Robert Recruiter, letting them know that I am still interested in working with them. Tomorrow of my tasks is to send out three resumes to new openings. Once a day I contact at least one person in my network to just say hello. Next week I will call Robert Recruiter and leave him a voice mail message, etc.., etc...  The point is to have a plan for how you will communicate on a consistent basis to new and past prospective employers and then stick to it.
For me, this is easy to do with customers (and I am not a natural sales person at all), I've learned by having a communication strategy, experimenting a bit at the beginning and paying attention to the results, that if I contact a prospective customer 3 times over 6 weeks, they will either have made a purchase within those 6 weeks or will never buy for reasons I can't do anything about. So I don't need expend any more time or energy on them. Although, I might follow up with them again every 6 months just to be safe because their circumstances might change over time.
I believe Mark recommends following up with job leads as many as 15 times. I'm not sure which podcast he says this in, but perhaps someone else can point you to them. Also, if you don't have the Interview Series, I highly recommend getting it.
AJ

When applying for a job, you must always expect some worst and unexpected. Don't always put any application you filed are with assurance.
 
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