I think it really depends on what the routine or trick is. If it's something like "My Pet Boris" then yeah, it will totally ruin the surprise if anyone remembers it (Which is iffy in itself). However, I have done the same trick to someone within the an hour and still surprised them. Something like Card To Pocket or Card Under Glass, when well done, build it up each time the card is revealed to be back where they thought it can't be. In these cases, when you say, "Do you know where the card is?" And they say, "Oh god, it's in your pocket isn't it. IT IS **** IT!"
I think it's really important to really think through the videos one posts. You can build a bit of a following by posting things like 20 second clips of a card transpo - but I personally think the best videos are ones that are planned out and scripted and blocked and all that. Like, think of Derren Brown's TV shows. There's usually segments where he does something kind of one-on-one, usually with a celebrity or maybe not. They are isolated, usually in interesting locations, and those were usually my favorite parts of his shows. Like when he did Smoke for Stephen Fry, or the bit with the undertaker in the crypt.
If you're posting up videos that are thought out like that, then it's more like watching a movie and probably won't come to mind when people see you perform the same or similar routines "in the wild" as it were.