Lifted from a website - again it is UK though.
Enforcing non-competition clauses (as opposed to non-solicitation) is quite tough (and expensive if going for an injunction). If you had no dealing with clients with your former employer and therefore no knowledge of them it is highly unlikely that the non-compete would succeed. See below for a legal opinion that I use as a reference:
In summary, a post-termination restriction will only be in restraint of trade to the extent it goes further than absolutely necessary to protect an employer's legitimate business interests. Such interests include, trade connections and trade secret information as you say, but have also been deemed to include a stable trained workforce - which is why non-poaching covenants have also been upheld.
Restrictions must be carefully crafted and reasonable in terms of length of time and area. In terms of time periods, restrictions of 6-12 months are acceptable where the former employer can show the employee has connections and influence which he/she has gained through their former employer and that the employer needs to keep them out of the market for that period of time to redress the commercial advantage. A wide area may be acceptable where the employer's business is not confined to one particular area (say, the City) but is a country wide, or even world wide business.
A restrictive covenant that is arguably enforceable, usually has the following qualities:
it is not excessive in time
it is not excessive in area (depending on the employer's geographical business)
it is limited activities carried out for a competing business
it is limited to activities in which the employee was involved
non solicitation/dealing is limited to clients with whom the employee had contact in the last 12 months of employment
non-poaching is limited to key employees with whom the employee had contact in the last 12 months of employment
If a new employer knowingly takes on a new employee who is subject to restrictive covenants and assists them (or turns a blind eye) in any breach of the restrictions then that employer may also be liable for inciting a breach. In fact, most companies will go after the new employer (they are generally worth suing and it can really damage relations with the new hire so has a nuisance value too).
Most non-poaching covenants (in common with the other restrictions) state that the employee should not "directly or indirectly" poach former colleagues. Hiring a head hunter to approach former colleagues is a form of indirectly poaching. It is difficult to police, however, a court is allowed to draw an inference and, if the matter came to court, any instructions would be discoverable as part of the process and the head-hunter is likely to be called to give evidence.