I'd say warlocks can be pretty nice defensively but their attack caps out at 38.5 damage/round (with magic item) or 31.5 without. Eldritch Glaive can help (3 attacks/round), but without some noticeable optimization (Binder + Hellfire mentioned earlier) they aren't that good offensively. They can have great defenses just using CA though.

I've ran 3 or 4 adventures where they had a high level warblade (2 below the party level) who declared them his cohorts (they knocked him out once, but since they were good guys didn't kill him but instead explained things to him... he remained arrogant but admitted they were his equals). He was fairly strong and badly built (used lots of Stone Power, although I hadn't noticed it couldn't be used when off the ground) and picked fights solo against elemental scorpions (it was fun watching the party scramble to rescue him and the primary healer who hero worshipped him for some reason). He could dish out damage and even grappled managed to knock out the scorpion with Moment of Perfect Clarity. The second one got him (also didn't use grapple right because we didn't know the rules for it well).

I've played a Crusader in a one-shot. Pumped his AC using Heavy Armor Optimization, Battle Armor, etc. But blew most of his starting wealth on intelligence for his armor and adamantine and the ability to wield a large war-axe (cause it was epic). Still had good enough AC that the slowed frost giant had to roll a 16+ to hit, and the dragon couldn't except on a 20 (used a variant dwarf with +4 dodge versus giants instead). Good HP, and excellent damage (Divine Surge).

I've also DM'd for a warlock from 12 to 20 (no FCII since it came out during the campaign and we didn't have it, also no ToM used). He was useful, used nothing from CM and only later on got Eldritch Glaive. Focused on defense. His damage was low, but noticeable and he was hard enough to kill it wasn't worth trying. He was 2nd strongest in the party till they recruited an army of cohorts, strongest being an Arcane Hierophant.

I've played a warlock levels 4 through 8. There were several full casters but they all were blasters. He was able to go into melee and survive longer than the duskblade (which isn't saying much since the dice tended to be fudged away from PC death to KO and the duskblade still died twice). He had Fey Skin feats for good AC, invisibility, and beshadowed blast with Ability Focus (Eldritch Blast) and a good charisma so he could keep one creature blinded for a good time.

From my limited experience... I'd say the warlock was useful, good, and hard to kill. But the ToB had more power. Both warlocks were defensively based, where as only one ToB character was. The 17th level warblade showed a noticeable increase in power compared to the 19th level warlock, but didn't outshine him since his AC was so low, he only ever used Moment of Perfect Clarity and then one other manuever (they made me run him and three other NPCs they'd picked up in addition to the monsters, he'd have done better to be a fighter) and the warlock had neat magical tricks. The crusader definitely had better damage/round (by over double) and better defenses. The warlock could turn invisible and had useful DR but wasn't as powerful or useful in combat. He was really fun to RP but I'd say ToB classes are probably a little better than warlocks in general. Hellfire warlock might stack up better (hellfire glaive? 48d6 with all three hits or 168 damage/round with chausable of fell power).