There are a lot of status effects that individually add a lot of flavour to an encounter, but like all things if used too heavily they get out of hand and turn an interesting encounter into a frustrating encounter.
As an aside there is a fine line between a hard or tactically challanging encounter and a frustrating encounter, and this line can shift depending on the number and type of PCs and also the players mentality or expectations.
Properties and effects like insubstancial, weaken, dazed, dominate and stun should be used sparingly. As someone has already stated an encounter where 1 or 2 creatures can weaken can be interesting and exciting, an encounter where 8 to 10 creatures can weaken can be frustrating and demoralising.
So good encounter design should point us away from using multiple creatures that cause similar effects, and point us towards the use of different creatures that cause different effects.
So instead of:
6 creatures that weaken
we should have:
2 creatures that weaken
2 creatures that daze
2 creatures without problematic effects
In my opinion the only issue with the "points buy" encounter design mechanic is that it can produce different results for the same total xp value. This shouldn't be a problem with a fair DM who wants to produce balanced encounters but it can cause issues for a DM who really wants to optimise his encounters for maximum synergy or effectiveness.
Compare the following level 7 encounters each with a 1700xp budget:
Encounter A
6x Wraith (level 5 lurker) (1200 xp)
2x Mad Wraith (level 6 controller) (500 xp)
Encounter B
6x Greenscale Darter (level 5 lurker) (1200 xp)
2x Greenscale Mystic (level 6 controller) (500 xp)
Both of these encounters is made of exactly the same balance of creatures of the same levels, one of them is a nightmare and one of them is potencially challanging but fair.
Encounter A has 6 creatures that are insubstancial, regenerate, target reflex and weaken with a basic attack, also with the ability to shift 6 squares once as a move action. Backed up by 2 creatures that each have an aura 3 that damages and dazes, with a recharge power that causes a PC to move and attack an ally.
Encounter B has 6 creatures that can potencially cause 5 ongoing poison damage and slow. Backed up by 2 creatures with an aura 5 heal for 3HPs a round, an encounter power that can immobilise and causes an area burst 2 to become difficult terrain, and a recharge power that dazes a single target until the end of its next turn.
So in conclusion I repeat that it is not the properties and effects that are the problem, it is the encounters built using them.
Personal opinion only:
My gut instinct tells me that some DMs cannot help themselves and feel that they should optimise as much as their player do, this can lead to badly considered encounters leading to frustrated players, whose reaction will be to try and further optimise and eek out every mathematical advantage the rules can give them, which in turn pushes the DM to try and optimise the creatures yet again....in a spiral of adversarial power gaming from both sides where the focus of fun has shifted from telling a story to exploiting the rules system to breaking point.