I have only been in the serious flying business for about a year now but a few stories to contribute how I recognized and met some fellow FTs:
I was hurrying to the lounge in AMS when I saw a lady hunched over her notebook at a cafe and typing furiously. On the screen was the easily recognizable FT board. I was tempted to ask her if she needed an invitation to the lounge.
A week before I was watching the football game GER vs. ENG in the STR lounge and had a chat with the English gentleman to my left. Went down to the gate, continued chatting and it turns out, he's a FT member. Turns out we've read each other's posts in the past. Arranged to be reseated next to each other and had a splendid flight talking about different products and experiences followed by a 1h stay in the AMS lounge. Yes, we did share pictures of airline meals. :-)
Sometime in December '09 I was again flying STR-AMS on the E90 only to find out that my usual seat at 11C was not available and went for 11D. The lady in front of me at the scanner was sitting on 11C so I remarked jokingly that she stole me seat. Continued chatting about Aberdeen, her kids, their flying practices (with FR, yuck!).
And then there are the not-so-serious flyers. I was kind of surprised to find out that amongst my friends and colleagues there are a bunch of FT account holders who do post much and don't fly much either but at least they got an account.
About being recognizable myself: I might be photographing the meal or be caught visiting the website myself. :-)