Are you sure about DMC4? I played it off the disc and the load times were pretty awful. After installing it, it had next to no load times at all.
Also, Guitar Hero Aerosmith shows about a 2-3 second load time decrease for songs. Which is good, because I hate waiting on music games for some reason.
Other games I've tested with comments:
Viva Pinata: TIP - Quick-selecting seeds, fertilizers, etc. they load up MUCH faster. Also, loads for shops and initial loads are slightly faster, though not noticable enough. Really all it felt was smoother.
Overlord - Load times between areas were maybe 2-3 seconds cut off at most, but it really wasn't that much of a difference. Overlord has such great loads anyway it didn't hurt.
Guitar Hero 2 - I've seen improvements in the loading times on this one.
Games I can't tolerate without installing: Mass Effect, Fable 2, Resident Evil 5