Impact of 'skill criticals' to balance in general is impossible to assess, as the effects of criticals are situational. Significance of skill crits also heavily depends on how much skill rolling is done on the table in general, in what types of situations and using which type of skills..
One effect is that your characters – and enemies, NPCs – can always try impossible tasks, and fail at mundane tasks. This has the downside that if the DM gets nasty or, heavens forbid, bored, then skill crits can be used to force simple task rolls that will eventually fail. They can also be used by PCs to their advantage, but forcing rolls on enemies while making none yourself is definitely trickier.
Overall, I feel that if there's a general rule that all skill rolls can have criticals, then it's bound to lead to bias (or even abuse!) of some kind sooner or later. You might start avoiding rolls or asking for them, depending on the situation – Essentially you begin to game the system.
Which leads to how we handle skill crits on our table (3.5, mind you). We have some special rules related to skill rolls. Most rulings try to follow the "rule of cool" and strive for good taste. We also like bit of chaos, so applying skill criticals when suitable is definitely used.
One "rule" we use is the catastrophic failure while trying something relatively simple, e.g. rolling 1 while climbing a ladder or balancing on ice. Characters can seriously injure themselves in the process...if the place and timing is right. The effect is heavily moderated by the overall situation. Dealing 1d6 fall damage to a 1st level rogue while in middle of combat due to a critical failure is different from dishing the same damage to a 3rd level rogue trying to climb a ladder to meet their love interest...while simultaneously creating enough noise to alert the spouse and the guard dogs. Failure in this way is not used as a tool of annoyance by the DM but as a tool for entertainment. Characters usually end up with few points of damage and exit the situation with a spectacular failure.
One other general skill rule we tend to use involves rolling 1s again with -20 penalty and 20s with +20 bonus (e.g. base skill +6, roll 20, roll next with +26, roll of 1 = 27, roll of 20 = 46). This way disasters and heroic efforts are possible but unlikely. It can also lead to hilarity, when the unexpected success leads to e.g. too long or too high jump or when your dwarf sinks in water faster than the anchor.