when flashing ICS roms, NEVER flash using the clockwork mod recovery included in some of the roms. only flash using cwm recovery in gingerbread roms.
i have used calk's ICS stock, and tweaked rom, and they have a few issues that i cannot live with every day. so i went back to calk's v2.9.2 because it is fast and has all the extra bells and whistles and tweakes (crt animation, hotspot hack, etc.)
to go back from an ICS rom, i just backed up my apps+data using titanium backup, but do not backup system data, it can brick your gingerbread installation. then use ODIN to flash gingerbread EL29 rom, then root and install clockworkmod recovery, then flash whatever rom you want.
bit of jumping around, but i have done it 5 times now and have the files lined up on my desktop so i just go in order and they get my phone ready to flash whatever rom i want.
edit: try ICS, just follow the instructions on this site, and research before you do anything. they are very nice! just not enough for me to sacrifice the few things gingerbread have working well (tethering for example) the browser alone is worth it however. stock browser in ICS is amazing