I've only taken and passed LPI-101 so far, and I found the test somewhat difficult because of some of the ancient technologies I was asked about. For example, what command would you use to find out the port settings for a serial port? Don't know, and probably haven't cared since 1999 when I first got broadband.
LPI-102 seems to be slightly easier, but only because I'm more familiar with the material there.
I can fill you in on LPIC-2 when I get there later this year.
I may be totally wrong here, but I think the majority of people stop at LPIC-2. While I'm interested in persuing LPIC-3, I don't know if I'll get there. I have heard that it is fairly difficult. That one will wait until I take the CISSP, and if work's still paying for it the RHCE.