1) Enoding MP3s with LAME: http://www.rockbox.org/twiki/bin/view/Main/GaplessHowTo says, that I should use LAME with the --nogap option
The simplest method is to use a format/codec other than MP3. For instance, Ogg Vorbis, Musepack and FLAC are all supported by Rockbox (except on the SH1 Archos devices) and are capable of gapless playback natively, without any special encoding techniques or workarounds. Simply encode the tracks per the respective encoder's documentation and they should play back gapless with Rockbox.If your format of choice remains MP3, then you can still have gapless playback by using any recent version of the LAME encoder, which will encode gapless by default. From LAME v3.90.3 upwards Rockbox will decode gapless, files encoded by older versions or other encoders are not guaranteed to playback gapless in Rockbox.
1) The --nogap switch is pretty much obsolete. I would be extremely surprised to hear that Rockbox still requires it.
2) What model and generation is your iPod? My friends' 3G Nanos have no problem with gapless playback. My 3G iPod on the other hand does, but Apple never implemented gapless support in that model.
3) pcutmp3 shouldn't be necessary unless you already have single-file mp3 images. I certainly wouldn't go out of my way to make them.
If your format of choice remains MP3, then you can still have gapless playback by using any recent version of the LAME encoder, which will encode gapless by default. From LAME v3.90.3 upwards Rockbox will decode gapless, files encoded by older versions or other encoders are not guaranteed to playback gapless in Rockbox.
I've done some experimenting with gapless on my touch. Foobar2000 with latest version of lame does it perfectly with just default (vbr) switches. I listened very critically for gaps, clicks or pops. I was using Nero aac before, and bad to switch because of very subtle gaps or pops on my touch. They worked fine elsewhere (including iTunes), just not on the touch.
Does the --nogap version indeed fill all MP3 frames while the "new" nogap relies on the information in the header?
The iTunes files play without any glitch while you hear a (very soft) click when playing back LAME encoded files.
There is something not right with what is going on with your iPod touch. I had a 1G 16GB iPod touch that played back files (Lame mp3, iTunes mp3, iTunes AAC, and Nero AAC) gaplessly just fine. I now have a 120GB iPod classic that has no problems either. There will occasionally be a small gap between older Nero AAC files but I can go back and play them again without any gaps. iPods themselves aren't gapless but rather rely on information added through iTunes. I believe this information is stored in your library.xml file unless you use iTunes to rip/encode the songs. What are you using to encode the files besides Lame (I am guessing foobar2000). Also, what version of Lame are you using and what build? I haven't had any issues with Lame CBR and VBR files from versions 3.97 and 3.98.2. I haven't tried older versions but I don't see why I wouldn't so long as iTunes scans the files for gapless playback.
Just for comparison, try foobar and latest version of lame with default options. Only change the vbr quality if you wish. I'm positive thee are no gaps on my 2g touch this way. I've listened carefully enough to hear the iPods volume change noise.