DB uses visible tongue in both the first kiss (the lights are brighter in the Pivot HD version and you can see the tonguing) and the Surprise bed one. They didn't do Hollywood fake kissing that is often below or above the lips (their kissing is definitely on the mouth). DB and SMG definitely were tonguing in some of their scenes. NB was quoted as saying that DB and SMG had a habit of kissing after cameras stopped rolling. And of course, they were known for playing gross-out games during their kissing scenes (they were definitely tasting in their kisses, so not fake). You can see them sometimes smiling in between kisses (Bad Eggs has a lot of that). SMG and DB had a lot of tabloids about them being a bit more than screen costars.
And yes, SMG is a huge Bangel 'shipper and is still friends with DB to this day. She's admitted having had a huge crush on both him and the character. She was very concerned that BtVS wouldn't survive without DB and dedicated her Teen Choice Award to him ("This is to my Angel. I miss you already, David.") in 1999 as he left for "greener pastures". The Prom is her favorite episode. Her Reddit AMA was her repeatedly stating DB and ANGEL to numerous Spuffy 'shippers begging her to change her answers about everything: better hair, better kisser, favorite 'ship, etc... She later had to do the same on Facebook with the same results. And she often crashed the Bones set for the catering and to visit DB while she filmed The Crazy Ones. They also apparently have ended up running into each other on poolside vacations, during which DB decided to get Freddie on Bones. Their daughters are also the same age. And SMG and DB tweet each other now on their birthdays. SMG hashtags
[HASHTAG]#myangel[/HASHTAG] and did a big collage of her and DB through the years on one of his birthdays.
She also had the set shut down because of her crying during both the breakup scene and "I will never forget." SMG was so distraught during the latter that she was begging for the ending to be changed and DB broke character and said "Shh, Sarah, please."
And of course, ED famously was tonguing DB in Enemies and asked if he could remove the fangs, only to have Joss ask why she was sticking her tongue down his throat.
JM's favorite romantic costar was Juliet Landau (so much so that his girlfriend at the time was jealous of him with Juliet when they watched episodes together and said she preferred David to make him jealous). He saw SMG as a little sister and had trouble in romantic scenes with her because of that. She didn't like being told that. SMG is not a Method actor and apparently made fun of him for not breaking character between takes (saying "I'm a tree!" about how Method actors pretend to be inanimate objects or their characters off-set), while she always did.
Alyson also made a controversial comment that SMG stopped caring about the show after season 3.
