I wouldn't say I'm disappointed by the offerings at all but yes the 2.26GHz mac pro definitely makes me feel very happy about my month and a half old 2008 3.2Ghz mac pro.
My analysis...
2.26 GHz Mac Pro (2009). A bit cheaper but just as fast as the 3.2GHz at multi-core processes but MUCH slower at single threaded processes by a considerable margin. For single threaded apps you're missing out on the raw clock speed of the 3.2GHz and these apps will suffer. My recommendation would be to hunt down a second hand or refurb 2008 model if you can find one. You'd be able to get the same multi-core performance of the new 2.26 unit and enjoy the extra speed available to single core apps.
2.66 GHz Mac Pro (2009). A full £1120 more expensive than the 2.26! That's a LOT of cash that could be used for the likes of more memory, faster hard drives (SSD), a 30" cinema display etc. Multi-core performance is much better than the 2008 3.2Ghz but single threaded process are still a tiny bit short of the 3.2GHz... all for an extra £1120! This is a FAST machine if you take advantage of multi-core apps. Much better than the 3.2GHz but still a little short on single-threaded performance for the price. Unless you use a lot of multi-core apps this isn't worth the additional £1120 imho. The money would be better spent on ram and/or fast drives.
2.93 GHz Mac Pro (2009). It's a monster. Much faster than the 3.2GHz Mac Pro in multi-core apps by a good margin and faster for single threaded apps also. This is a powerhouse but this super computer comes at a HUGE price. In the UK this config is DOUBLE what I paid for my 3.2GHz 2008 mac pro.
Basically you have to look at the software you use. If you're running efficient multi-core apps that USE all cores properly and time is money the 2.93 will pay for itself in no time. An amazing choice if you can afford it.
At the opposite end of the spectrum you have the 2.26GHz dilema as stated above. This machine will probably be the main choice for most users. The additional cost of the 2.66 and 2.93 is substantial and you really have to balance your needs over wants to make sure you don't just waste money.
My view is maybe slightly biased since I just splashed on a 3.2GHz mac pro just over 6 weeks ago but I honestly think this machine is the best value/performance you can get. This machine may not have the fancy new architecture BUT it's just as fast as the 2.26 for multi-core performance and MUCH faster for single threaded apps.
Hindsight is always a great thing but if I chose to wait for the new macs I would have been pretty pissed to find out that my new option was the 2.26 considering the hit in single threaded apps over the 3.2.
I'll say it again but there's something nice about having the fastest mac pro from 2008 rather than having the slowest mac pro 8 core from the 2009 refresh.
PS. Just wanted to add that since the ATI Radeon HD 4870 is available as an upgrade kit for 2008 mac pros... again what else can I say