Garmins relativley modest overall contribution to sirf revenues have already been priced in months ago. Much of sirf's valuation rests on massive sales to the handset market which may or may not occur. It is certainly happening a lot slower than many had hoped. There are also subsitutes for sirf's products with more on the way.
NVT is hurt in the short run by the switch from built in systems to inexpensive PNDs that have lower margins. However, it looks like the amazing growth in PNDs will offset any losses in built in but it will be cyclical. NVT does not recognize any revenue until the Garmin unit is sold either to the retailer or the end consumer I not quite sure and so there will be a lag between the two. In the long run, if NVT takes care of Tele Atlas it will be a monopoly. I like the odds.
Also, Garmin sells many products that do not have NVT maps or have sirf chips. The whole marine rollout was not a particulary boon to either NVT or sirf for example.