When I join a PUG with my healing-spec cleric, everything is roses. No need for any preamble. I know I can handle pretty much any healing required for the quest and I don't mind it because thats what that cleric was built for.
On my turning-spec cleric 4, its a little harder. She's great at turning undead and great at being a mobile shrine (because she has lots of turns) but her healing is not so hot at the moment. She has maximise and will get empower and DL next level. She'll get the healing enhancement line eventually so she has some decent healing capability but she ain't getting the healing crit line. Mainly she is geared towards turning, zorching undead.
If its an non-undead quest, I'll answer the tell with "This clr is turning-spec so shes OK on the healing front but not fantastic, is that cool?" and then repeat in-group with the addition "Obviously I'll do everything to keep you guys up but if you're low on HP, don't be shy to use a pot!".
If its an undead-heavy quest I say "This clr is turning-spec so I'm going to be spending her turns and SP destroying undead. I can throw out the occasional heal but I'm not watching red bars so everyone should have a way of healing themselves, is that cool?" and then repeat in-group.
What do you guys say when you join a group with your BC/offensive caster/turning cleric? Do you flat-out refuse to heal or what?