We only tested dd20, and that was because she had both anxiety and giftedness and we really didn't know what was going on. We did the full psycho-social-intelligence (and whatever else you can throw in during a full day of testing, which we didn't even realize at the time included IQ). Yeah, it was helpful (not so much the IQ) but it wasn't as if we've done a lot with it. It did help during IEP meetings, because the school was able to evaluate her more fully. As far as our next three kids, we haven't gotten IQ testing and don't plan to. I just think that there is so much more to success than one test - we know they are smart and we've been lucky enough to have the school also believe that. We did "quick testing" with dd8 to get him into a summer class with CTD a few years ago and we had ds10 take the EXPLORE last year, but those were more about a specific purpose (in the case of ds10, we were interested in figuring out where he was at, and the test was a huge help - since our school district also uses it, it was a great tool for advocacy as well).
Dd20 has felt at times the "weight" of being PG, along with having social-emotional challenges. She's now a senior in college and sometimes feels like she hasn't lived up to people's (our?) expectations. It's sad that she is going to graduate from a decent school, full scholarship, BS in biology at the age of 20 and she is worried that she might disappoint us. THAT is the downside. I'm not against IQ testing by any means, though. I just don't think that any couple of hours in any child or adult's life is really going to tell you of what they are capable. I'd rather have them focus on always continuing to work hard and challenge themselves.
Anyway, just my two cents,
Theresa