The big weakness of Psi Warriors is the need to buff up before a combat. You don't want to get surprised, and you need a few rounds to put up those 1 round/level powers.
Yeah. I tried playing a Psi Warrior in 3.0, and as much as I loved the concept, I found the above situation to be so miserable, that it was unworkable. I seemed to find that either I could go directly into combat, and essentially I was fighting like an un-buffed cleric, or I could stand back and buff myself. The first option kind of made the whole Psi thing pointless, and the second created one of two other problems. Either my compatriots won the fight by the time I was in it, or the bad guys would bring it to me and I still didn't get my buffs in.
I've purchased the Expanded Psi book, but haven't had the option to test it. It looks better on a read, especially w/introduction of immediate and swift actions, but I haven't tested it yet. I'll be checking this thread with the same interest as the original poster.