Although I've never played an ECL character, I've been in campaigns with one. Let me second the apparent consensus here.
1. ECL characters aren't good for spellcasters.
2. ECL characters are weak at low levels. (The previous post indicated that they may catch up somewhere around level 8 or 9 and possibly surpass their ECL +0 brethren later. . . but you have to live long enough to get there first).
My experience is this. One of our groups oddball power gamers (I call him this because he has a habit of picking the race/stat combinations that give his characters insane strengths, etc. but seems to fail to make proper use of these or take into account their weaknesses resulting in characters that should be effectively seven levels higher than the rest of the party proving only one or two levels more effective than the rest of the party in practice). We were playing Return to the Temple of Elemental Evil and our DM let us create 4th level characters. He picked a 1st level half-dragon half orc barbarian with a 28 strength. Everyone else chose an ECL 0 race (elf cleric, human fighter, elf fighter, human sorceress, human ranger/druid). He has proven to be able to dish out damage very effectively but is unable to take it. He was the first character to die and would have died again had he not cowered in the corner during the party's fight with the greater water elemental (which ended up killing the human fighter and nearly killing the elf fighter and the ranger/druid). Had he not made his reflex save in the first major encounter, he would have died there as well (after making his save, IIRC, he was at -7hp). He certainly has the ability to dish out damage quickly (1d12+13 with a greataxe or 1d12+16 while raging) but he would dish out even more damage on a full attack as a 6th level barbarian with a 20 strength (what he'd be without the template) (2 attacks for 1d12+7 (+10 while raging) each) and his saving throws wouldn't be nearly as much of a liability. (Personally, I doubt the character will live to see the level it will reach parity with a non ECL character).