Are you kidding?
A +4 to hit bonus that applies in basically the most common circumstances is a waste?
Not everyone has a bad touch AC.
Bye
Thanee
Let's look at the "investment" being made to get the benefit. Remember that a warlock gets no "bonus" feats so is essentially feat starved.
First you need Point Blank Shot (+1 to hit and damage w/i 30 ft)
then you can take precise shot (ignore the penaly for shooting into melee, essentially ignore the -4 to hit).
Note that when making a touch attack in most cases (not all, but clearly most when there is a lot of melee going on) you already get to ignore the armor and shield and natural armor bonuses to AC - which will usually get at least a +4 on your net attack in the first place..
If you multi class with fighter - using the fighter feats to pick up PBS and PS is not a bad choice, but trading warlock levels to do that is almost never worth it.
Getting feats like:
Magical Aptitude (+1 to spellcraft and UMD checks) is better for a class that excels at UMD (assuming the campaign is not a low magic item device one)
Dodge - always handy, even though the warlock has a better AC than does a wizard/sorcerer.
Improved Initiative - always good for a non-healer spellcaster
Skill Focus - UMD (don't underestimate the power of someone who is as good at UMD as is a warlock)
Any item creation feats (especially wands and wonderous items) work really, really well for a higher level warlock (again it depends on the population of magic items in the campaign)
Weapon focus (rays) is better than precise shot, but only available at 3rd level (that is the warlock can't meet the +1 BAB prerequisite at first level)
A warlock is not a primary anything.
He is decent at ranged damage, over many encounters.
He is great at UMD
He is great for detecting magic (saves spells for spell casters in the party and the sorcerer won't need to use a known spell to take it)
He has almost no support capability since almost all of his invocations are self only types and no "buffs" - but this is where UMD can come in really handy.