cortland wrote:I'm curious now, how much web traffic does a web comic need to be considered "popular?"
... or better still: potentially profitable?
Profitable is easy. As mentioned earlier in this thread, Randy of Something Positive said that the threshold was 4,000 visits per day for one type of ads. That might vary depending on the type of ads you run.
'Popular' is a different thing. Here are some numbers for big webcomics that I've pulled out of my ass.

(Actually, I've taken them from either rumors in this thread or from the sites' own advertising pages. Where they specified 'pageviews', I'm assuming an average of 4 pageviews per visitor, which is a figure given by one of the sites listed.) Consider all these numbers to be vague, rumored, estimates:
*Ctrl-Alt-Del: 250k/day
Penny Arcade: 200k/day
*VG Cats: 120k/day
PvP: 50k/day
Something Positive: 38k/day
Schlock Mercenary: 20k/day
Ghastly: 15k/day
Yirmumah: 9k/day
Evil, Inc: 5k/day
(*CAD and VG Cats numbers were taken from their shared advertiser's site. I don't believe them. Or rather, if they're right, then Penny Arcade's numbers are way wrong, IMHO.)
As a general rule of thumb, it looks to me that if you get into 4 digit visitor numbers, you're pretty popular. Somewhere between 4 and 5 digits is when you become profitable.