I used a Transcend 150x 4GB SD (not SDHC) card for the first time the other night in my Soundbridge Radio. The SB recognized and played all songs on the card just fine, although it didn't recognize the time/duration of the songs at all. The time bar was empty and didn't progress at all during song playback (not a big deal, really).
If it's any help, the SD card contains regular unprotected mp3s, transferred over from a laptop by simple drag copying. When used in my Palm Treo with the latest version of Kinoma Media Player, the time/duration of the songs is recognized, and the time bar progresses just fine during playback.
My music is also displayed alphabetically by title. I haven't tried to group them in folders (such as by genre), partly because I read somewhere that the folders wouldn't be recognized, either by my Treo or by the Kinoma Media Player.
Also, I read on one of the Treo message boards that the SD format for these memory cards can only go up to 4GB max storage, due to the formatting of the card. Anything above that (like 8GB) has to be in the SDHC format, which (I believe) requires some kind of additional software capability for reading/writing that is not built in to my Treo (and may not be in our Soundbridges either).