SBing is fine, so long as you are accepetable with it, meaning if you put on every single item as white and a level 48 weapon for SBing you are pretty much hindering your performance greatly , if it's WP or AK, sure you can still "beat" it but crawling through the dungeon and suffering along the way because someone decided to full SB every slot is where it gets stupid.

Usually when i SB ( mainly as healer) i use the rings/earring 1-2 slots on armor, never my full set and most certainly not the weapon as that is where your biggest performance comes from.

i assume it is the same as DPS. Just be moderate with it and it shouldn't be a problem. If i do see someone in full out SB gear, pretty much making it a 3 man run then i will probably just leave or let them know they are asking to be carried. if you seriously have to do a full set you can just go solo. I don't think being reasonable is to much to ask.