but the server iss so far better than apache, at least for VPS there is no comparaisons possible with apache
Well since you have first-hand experience with this matter maybe you can give us a real world example of how the installation of lighttpd has resulted in a tangible improvement to a site's functionality that isn't based on some unsubstantiated evangelism and provide a little more info on how you came to reach these conclusions over the course of just a few short days. "Better" is a relative term, and a handful of BitTorrent trackers, free image hosts and Romanian dating blogs is not really all that impressive since those sites don't really do very much, and nobody over the age of 13 is going to get all that upset when they go down (which they do; frequently).
YouTube is certainly a prominent example, but they had to do quite a bit of work modifying the lighttpd code to get it to do what they wanted and that divergence is going to translate into monumental headaches when it comes time to upgrade down the road. Whether or not lighttpd was the "better" choice for them is something only future YouTube employees who have to maintain their patchwork monster can answer.
lighttpd has some advantages over Apache, but as a product, it's quite immature, and by and large people use it out of a desire to look cool and impress kids on IRC with a paper airplane PNG on their blog. Things like this might be important to say, DreamHost, but most people just want a solution that works more often than not.