Examples include:
- Raise dead. In no campaign I ever run will a PC be able to bring people back from the dead at level 8 by spending 500gp.
- Portal spells. If your not familiar with them and don't plan around them, you have to pull out a macguffin to stop PCs from ruining the plot you just made by teleporting from A to B. This rules out most "oh no we are lost in the forest" or "how will we get out of this sieged village" style adventures.
- Social and language rituals. There seems to be little point in buying feats regarding learning languages and comprehending writing when a simple ritual can do so much of it.
- Animal messenger, Sending etc. These just ruled out any "must get this message to the king" style adventure.
Rituals are powerful to the extent of changing the actual plots that the GM can use without hand-waving away their usefulness. Keeping on top of all the options that the players have takes a lot of work to not find a plot made impotent.
I agree that the DM concerned about the integrity of his plot or world design should keep an eye on what rituals are allowed in play. For me the Portal rituals are probably the biggest issue, they assume the existence of a functioning, widely accessible, portal network in a way which doesn't really fit any of my 4e campaign worlds, and would have major effects on the economy of any world - eg high value trade through portals would obviate the need for ocean going treasure galleons, hence a 'Spanish main' pirate setting becomes impossible in a portal-world. I'm looking at limiting the range of portals, and in most cases portals will belong to secret hidden conclaves of wizards, not something accessible to the general public.