i just found a "new" seven which i've never seen mentioned anywhere before (or i'm just blind) in "a converted church in venice, italy":
after you've caused the volcano to erupt and the lava has risen up you come out at the starting point with the 2x and 3x recharger with an elevator (if you've chosen to go up this way). recharge to 3x and dive back down the elevator shaft. you'll see a door at the right hand side of the big cave. behind this door there is another door, which is locked until the lava rises, then it opens slowly. you now can access it and ride up another elevator leading you to a room with a 3x-recharger and - yes - 7! invincibility-powerups. i could bite my arse that these are not accessible earlier (or are they? tell me!).
after working through this level so far these thingies are absolutely useless except for... another display of "7".
any comments?
(well,i guess i'd better shut up 'cos probably i'm the last lamer on earth who found this secret and wondered why there are 7 invincibilities in this room...)