There are a good chunk of guys that are boosting their LS1/LT1s with pretty good success. The problem is that with a few mods, there is plenty of power already from a N/A engine (400-600, depending on what you do, can get up to 850ish if you need an N/A engine with massive power). So boosting is left to the guys with the need for 850+ horsepower. I went to a 'vette show in Carlisle and saw a few turbo’d vettes, and there have been a few instances of Lingenfelter 427TTs in magazines and such. One C5 was in Motor Trend in a “vette vs jet” shootout where the cali-legal vette did a sub 2 second 0-60, and this isn’t the most powerful TT vette I’ve seen, so I imagine there is faster out there.
I saw a Turbocharged LS1 240sx a while ago. The turbo was one of the retardedly large Supra-ish turbos that was as big as the engine. I’ve seen a LT1-TT 240z on youtube.