How exactly did Yakov 'steal the heart' of Lavan?
Targum Onkelos and Targum Yonasan: By simply not informing him of his plan to leave.
Seforno: By pretending not to know that Lavan had accepted his sons' Lashon ha'Ra, and not to notice that his friendly disposition towards him had changed.
Tosfos ha'Shalem (1, citing R. Efrayim): Lavan planned to steal all of Yakov's property. Since Yakov took it, it is as if he stole Lavan's heart.
How could Yakov leave his host of twenty years without saying 'goodbye'?
Seforno: He did not do this out of ill-manners, but because he was afraid that Lavan, with the help of the people of the town, would steal from him. 1
Why does the Pasuk refer to Lavan here as "Lavan ha'Arami"?
Ramban (later): To teach us that, despite the fact that Lavan was a master trickster (a sorcerer to boot), Yakov succeeded in 'stealing his heart'. 1
Seforno: To explain why Yakov stole Lavan's heart (Refer to 31:20:1:1). Because, had Lavan realized that Yakov was aware of his feelings, he would have placed obstacles in his path to prevent him from leaving.
How could Yakov have informed Lavan that he was fleeing?
Targum Onkelos and Targum Yonasan: "Bore'ach" means (not that he was 'fleeing' but) that he was 'leaving in haste'.
Oznayim la'Torah: The Pasuk means that Yakov did not inform Lavan (not that that he was fleeing, but) because he was fleeing'. 1