I bought an 2008 G35xS 3 days ago... Love it, want to try out XM but i saw this package listed on the XM radio site. Is this XM NavTraffic package that is 3.99 a month required for this vehicle??

No, it is not required.

I might not have been clear... Will I still get traffic updates and such on the GPS without this package?

Yes, your navigation will work fine without the real time traffic. The nav system comes with the car (if so equiped).

Navigation / Real time traffic / and XM Radio are all independent of each other, but Sirius/XM does have bundles that combine XM radio with real time traffic.

Navtraffic will give you overlays on the navigation screen showing traffic conditions similar to what Google Maps does. It will also reflect advisories on certain routes, but 100% of its functionality depends on what kind of data is available to them in your specific area. I'd suggest checking out SiriusXM's website and seeing what they list for your region before signing on for the extra $4 a month.

I live in an area with full coverage on most of my commute, and my 3 month XM trial option included Navtraffic. My problem is I keep forgetting to check it before I leave for/from work.

Agreed, check out the SiriusXM website to see what areas are covered. My commute is covered with the Green/Orange/Red flow lines, which makes my commute 100% better. If my area didn't have the traffic flow lines, it probably wouldn't be worth it for me.