I didn't, and found out most of my neighbors got a lot more, HOA fees paid, etc. However, the guys that built it did do a lot of extras for me anyway, wrong stair rails (OOPS, the more expensive ones), built some shelves, etc. I did end up with a lot thrown in by the builder because sales were so slow they were upgrading stuff. Several people told me to use a Realtor, if I was doing it today, I would.
Starting Score: EQ 679, TU 697
I'd definitely say from my experience that the best way to negotiate new construction is having a realtor as your representative. Also, spend the time to actually figure out what "upgrades" you want and then have the builder price it out right then and there BEFORE you submit your offer. While I do agree that it may be possible that some companies won't budge - what I think is even more important given today's market and economy is that companies WILL negotiate as long as you're not extremely unreasonable. IE - asking for $50K in upgrades but lowballing the offer such that you're not offering to pay any of it and on top of that asking for closing costs.
Anyways, my experience was that hubby and I spent about a month looking through all the different floorplans as well as various upgrades in the homes the models. Like, we even went to another community built by the same builder since there was a floorplan we fell in love with but wasn't built at the place we wanted to build. Then, hubby and I sat down and figured out our "must haves" as well as "it would be good as long as it's not going to break our budget". Now, when we talked to the builder's rep, we didn't let them know we had two separate lists - we just told them this is all we want, price it. They knew up front that we were working with a realtor. So the lady gave us a pricing sheet to tell us what the final cost would be. That was great because we could then decide to take things off, etc. in the privacy of our own home. After that, we met with our realtor to show him all the paperwork we got from the builder.
Since I was due to travel quite a bit, I made sure to talk with honey before I left town so that way if our realtor called and said "this is the counteroffer", I could tell him right away what our next step was. That being the case, we had them price out everything we wanted and the total price was just under $260K. Expecting to negotiate, our realtor put in an offer of $245K and $5K closing. The builder accepted and it took all of my might to not cry while I was at work since I snuck out of a meeting when I saw that my realtor was calling me back 
We're in NC....The house we're having built is 4 bedrooms, 2.5 baths, .25 acres, we did green updates - rain barrel, R-15 wall insulation, radiant roof sheathing, R-5 XPF in master, R-38 blown ceiling insulation, tankless water heater, double flush toilets, 18 seer ac unit, recycled carpet - and other stuff like granite in the kitchen, hardwoods throughout downstairs, screened porch, sod/irrigate rear yard, stainless appliances, finished garage, tile in all the bathrooms...
So I'm not listing all that stuff to "brag" but to really show the point that especially in new construction, just like in life, "you don't get if you don't ask"...The worst thing the builder can tell you is no...While it no doubt took awhile to go through this process since we did decide to have them price things out up front and of course, sometimes we had to wait to get the cost on the greener updates - in the end, I'm happy we were "patient" up front because before we stepped foot in the Design Center to pick out colors, etc. we already knew that everything we wanted in this house had already been negotiated and so it wasn't like we had to walk around with a calculator to make sure we weren't blowing our budget...
Good Luck!
Shelly
Starting Score: TU-720, EQ-692, EX(FAKO)-766