It's interesting to see the disparity of opions here - LOL. Some say take the money and run, others suggest waiting it out...
Anyway, I am comfortable waiting for a 'better offer' at this point. I have had quite a bit of interest in this domain and this offer, I feel, is only the beginning (it's NOT the first offer, but is the highest so far).
I am willing to wait 10 years if that's what it takes.
Imagine if .tv gains even more popularity than it has right now - I think 'invite.tv' could possibly someday go for 5 figs!!
One last note: Several years ago I had 2 3-letter .com domains and I often posted them for sale requesting what many people thought were 'outrageous' prices. I had MANY, MANY offers where people on the boards said 'take the money and run' you'll never get your price etc etc. Ultimately, I was proven right and, as it turns out, it was very prudent of me to wait...I STILL probably sold to soon, but the BUYERS were even more of a visionary than I was when it came to predicting the future value of some of these domains.
And it PRECISELY THAT type of buyer I am looking for for invite.tv - someone who has the forethought to realize that, hey, in 10 years this may be a 5-figure domain, let me offer that guy 5 or 6k now because that's about the absolute MINIMUM I would entertain for this domain. And that is TODAY. Next year (just like with my former .com's) I'll want more

.
Thank you all again for your advice and comments!