When an enemy fails a Will save against one of your technomancer spells, it takes a –2 penalty to saving throws and AC for 1 round. When an enemy succeeds at a Will save against one of your technomancer spells, it takes a –1 penalty to saving throws against your spells for 1 round. A creature can take only one penalty from a mental mark at a time.
Note that it specifies "a save" not "the" save or the first save. So for spells that can lead to additional saves on subsequent rounds, this can be a somewhat lasting debuff on top of those spell effects.
So far I can only find three spells this interaction applies to, but that may grow.
1. (Mass) Baleful Polymorph (1-6/4-6): forces at least a few saves regardless of success/failure, and if they keep making their saves (after the first failure) it can go on indefinitely. Definitely the strongest one to combo with (and it imposes its own penalties to AC and reflex saves) but has a 1 round casting time.
2. Inject Nanobots (2): Not good. Requires first a touch attack then a fort save to be failed before you get to subsequent round will saves. As soon as it makes one of those the spell ends.
3. Mental Block (3): Medium range, multitarget, the only downside is that subsequent saves do end the effect. Compare to Slow at the same level, which is one and done. This is pretty good synergy if you can't afford the spell level or casting time of Mass Baleful Polymorph.