I guess this depends on your definition of "lossless". IMHO this term is pretty overloaded. If by lossless you mean that it's possible to merge splitted parts togegher so that the result decodes to the same thing then I have to admit that this is currently not possible with pcutmp3 (joining not yet implemented but possible theoretically).
Parts that have been generated via simple frame-wise cutters can usually be joined via
copy /b part1.mp3+part2.mp3+part3.mp3 all2gether.mp3
(let's forget VBR headers for the moment)

However, in certain cases it is desirable to use something like pcutmp3 with its mentioned features (for one it handles inter-frame dependancies correctly resulting in files that don't let the iPod choke on playback). To my knowlegde there's nothing comparable out there.
If by lossless you mean, that the mp3 data is NOT reencoded then: No, Most of the mp3 cutter/splitters do it losslessly (including pcutmp3).
Let me throw another buzzword in the ring: gapless
It really depends on what your player does. If you use mp3DirectCut and the player just concatenates the files on the fly while playback then your playback will be gaplessley. I believe the Rockbox firmware (for mp3 porties) does that. The catch: Play'em out of order and you'll hear glitches due to bitreservoir dependancies.
If you use Foobar2K or XMPlay32 (these support the LAME tag) I encourage you to try pcutmp3. I'll be perfectly gapless then (LAME tag support is important).
Sebi