It's very common in spellcasting of intricate spells (for thaumaturgy complexity, ect) to spend multiple actions creating aspects... while these are done in a few quick rolls, narratively it can take... weeks, longer?
"I research the demon in a library" "ok it takes you a few days, roll lore"
"next, I use my resources to buy quality ingredients" "roll resources, and wait for them to arrive in the mail."
"Now I'm going to gather a few hedge wizards to help out" "roll contacts, you'll need to set a date for the ritual now so they know when to attend"
"ok, well I'd like to spend my remaining time until then in meditation, purifying my mind." "roll conviction."
One spell, four tags, a few weeks... and that's perfectly normal for a spell like that.
Equally common (as in, I've seen it when I've played and when I've GMed, and read about it on the boards and blogs) is the dogpile:
Four people surround the victim.
Attacker 1 makes a declaration (fists vs fists, he doesn't know the particular martial arts I am using, and isn't ready for it), and a maneuver (athletics vs athletics, better positioned).
Attacker 2 makes a declaration (fists vs fists, he doesn't know that I am using a different martial arts but have long practiced with my buddies to create a cohesive fighting style as a squad), and a maneuver (athletics vs athletics, flanked)
Attacker 3 makes a declaration (fists vs fists, I've been in a lot more gang fights than this dude and am better prepared for this), and a manuever (athletics vs athletics, surrounded)
Attacker 4 makes a declaration (fists vs fists, the opponent is unaware of the particular attack my buddies have set me up for), and tags every available aspect. If all landed, he now tags seven aspects for a +14 on his roll (although it's likely that maybe half worked?), and assuming he had, say, a +4, he now rolls and adds 18, resisted by athletics, fists, ect. The opponent is easily getting hit for 10-20 stress, inflicting consequences and probably forcing a concession.
So, I'm probably more okay than others might be if the same player wants to spend a few rounds doing something similar, only alone. Stealth through the area, getting not only an aspect but also the surprise attack benefits. Use your weapons skill to analyze the opponent's threat level. Use your lore to see if you can detect anything abnormal, and make guesses about the opponent's strengths and weaknesses. Use your guns skill to aim. Snipe from cover with a +8 on top of your skill of 5. Tag 3 aspects as well, so now you're rolling and adding it to 19... sounds like a good stealth kill to me; if you can pull it off given that every roll will be opposed.
Creating aspects for one big hit is the way combat seems to work best. It also allows your ninja PC to feel important for spending those few rounds, well, being a ninja, instead of jumping out and swinging each round, which becomes optimal if tags are limited.
IS there an upper limit? Hrm, usually the situation only allows so many tags. If someone seems content to just sit back and try to pile up tags, then I begin logically restricting other tags due to the opponent's actions, as well as toss something in to make the situation more urgent.