I have had problems with mages in my campaigns (and in another one) recently.
We have this one guy who always plays sorcerers. Always has a low Charisma score (eg 16 at 15th-level). He always has a high Strength and Dex and uses melee weapons ... but has low Con, refuses to use buffing spells except mass enlarge person ... he died in my high-level campaign but gets lucky in other campaigns.
Once he saved our butts in melee as a 3rd-level sorcerer ... but we had to convince him to sit still and let us heal his 1 hit point behind! (He got smacked down early in the combat.)
He also tells us that the DM should roll for falling damage when he jumps out a window! Um, anyway...
Okay, I've had two other wizards in my high-level campaign. It's 28 point buy, so some of these issues are my fault.
The effective wizard decided to nerf his Dex (to 13) and Wisdom (to 8) to get an Int 18 and a high Con (being a gnome and all). I wasn't too happy about that, but it was my fault for not using the default 28 point buy. The only real worry is his sunburst spell, since it can blind multiple opponents and has a good save DC because of his high Int. Oh yeah, and apparently his opponents are blinded forever (even he agreed I should nerf the spell).
The other wizard was only there for one session. Like the above wizard he's pretty smart and uses tactics ... even when I had to remind him about the haste nerf. Alas, he picked low physical stats (all three) to boost his physical stats, and so has low hp, AC, Reflex and Fort saves ... seriously, if he were to fight a prepared enemy he would die quickly.
I've done this myself too, of course. I played a ranger in a low-level campaign. Foolishly, I chose Weapon Finesse instead of Precise Shot at 1st-level. I'm getting close to 3rd-level and am still regretting the decision. I will definitely take Precise Shot at 3rd-level. Definitely.