Early July 2004. DEN to SFO. early am flight
Tarmac wait/hold at DEN > 7 hours.

Ok, so SFO does get fogged in and more than it's share of ATC holds,
but not usually mid/late mornings, or in July.
Nonetheless, I wrote it off as a one-time fluke/bad-luck

Two weeks later: Late July 2004. DEN to SFO. early am.
Tarmac wait/hold at DEN > 8 hours.

"When pigs fly, chicken have teeth, a week has two Thursdays,
hell freezes over, the sun rises in the west, and frogs grow hair,
I will once again fly United airlines"

...is putting it mildly.