I recently listed to a great Podcast on VAAI from Greg Knierieman over at the Storage Monkeys website.  You can find the podcast here  (the whole site is well worth a visit).
He was talking with Marc Farley (his co-host, from 3PAR), Chad Sakac (from EMC) and Chris Evans (the 'Storage Architect').  The topic was VMWares newly announced VAAI.    

To quote from the podcast, VAAI is a set of APIs focused on the VMWare kernel to off-load various functions onto the storage.
To get the newly announced VAAI functions you need to upgrade to the newly announced VSphere 4.1  and you will need to upgrade your storage hardware firmware to a version that supports it (when such a version comes out).
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Some of the major new functions are:
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Hardware accelerated locking  (to avoid the need for ESX to use SCSI reserves when doing meta-data updates)
Hardware accelerated  full copy (to help VMWare clone data without having to do lots of read and writes)
Hardware accelerated  zero (to avoid the need to send vast numbers of 'empty' SCSI write I/Os to zero out blocks)
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Given who was on the call, the conversation focused mainly on what EMC, 3PAR and to some extent what NetApp are doing in regards to this development.   
Apart from some (good natured?) digging at HP, no other Vendor was really mentioned.
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One thing that was mentioned was that some storage hardware architectures will lend themselves far better to VAAI than others.
In particular Chad mentioned that he would expect fullcopy and hardware accelerated zero would work better on V-Max than CLARiiON, due to hardware architecture differences that also benefit 3PAR. 
I found that a really interesting observation.
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What wasn't mentioned on the podcast was XIV.
So to be clear, the architecture of XIV lends itself very very well to the changes required to support VAAI.   
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To give an example of how we have done this with other vendors, XIV firmware 10.2.0a brought in support for Symantec Storage Foundation Thin Reclamation.
XIV support for Symantec's Storage Foundation and Thin Reclamation API means that when data is deleted by a user who uses the thin provisioning aware Veritas File System (VxFS), XIV will immediately free unutilised blocks and reclaim such blocks, rather than leaving them with 'garbage' data that wastes space.   
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So have no doubts, XIVs architecture is very 'friendly' to the sorts of things VMware are trying to achieve with VAAI.  To underscore this, Chad also said that a VMware goal was that VMware admins should need "no requisite knowledge of the underlying infrastructure for any task".   The goal is to use policies instead.  Given this goal, XIV is also a perfect match.   With XIV there is no need to think about raid types, raid sizes, disk types, disk sizes, LUN allegiances and trespassing, controller workload balancing or hot spot detection prevention or correction.   All of these concerns simply don't exist.   
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The good news is that XIV is working with the VMware Reference Architecture Lab and the statement of direction is that we will announce VAAI support for XIV later this year.   XIV continues to be an excellent choice for VMware environments and when VAAI support is added to XIV, this will only improve.
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Finally, Chad made a great quote on the podcast. He said:  "Never trust any vendor when they talk about what other vendors are doing"
I think this is a really great statement and one that everyone should take to heart.