I'll put down a few words, so feel free to discard them at will.
We've implemented a similar solution with two 7009 switches with F2 modules, 5596UP switches and 2232PP FEXes, and there are a few things to be aware of with regards to the 7k platform in general and the F2 modules in particular.
1) The F2 mainly a High Troughput line card, whereas the M series is for Features. This means that you need to carefully consider what you want to do and figure out if the F2 will do it for you. For example the data sheet says it does NetFlow whereas the latest software specifically says it _doesn't_ do it on the F2. TAC says to wait for 6.1 release in Q2Y12.
2) IPv6 on NX-OS (caveat: on 7009 chassis with F2 module) is missing a few features such as RA priority and suchlike. Not sure if this is coming or not, but it's a bit of a bummer if you wanted to make one chassis the primary unit for a particular VLAN (both v4 and v6).
3) We're currently engaged in a TAC case concerning some problems we're having with HSRP and DHCP relaying - the DHCP discovery is forwarded to the server, but in some cases the reply doesn't reach the client. In this particular case the servers subnets are routed on both 7009 switches but the primary switch for the client VLAN might not be the primary for the servers, causing a degree of asynchronous routing (long story). At the moment it looks like a ARP or layer 2 issue but we're not sure yet.
4) NX-OS is very much into the new NetConf management way which means many of your old SNMP tools won't work (this goes for both 7k and 5k). DCNM is not a very mature product as far as I'm concerned and leaves a lot to be desired. If you have SNMP tools you need to make sure you can use them with the new platform - the MIB support on the 5k is laughable, for example. If you do everything by CLI and spurn fancy GUIs as toys for children you're golden
There have been a few other minor niggles, such as the mgmt0 interface on two 5k switches actually changing MAC addresses after a software upgrade (which meant the NMS thought they were down for a good 30 minutes until we could investigate - the MAC addresses had been incremented by 1 for some reason). They also had a _serious_ bug in the 5.0(something) version of code for the 5k that made the vPC pretty much useless. This was fixed in the 5.0(something + ohcrapIcantbelievewescrewedthisup) release.
I'm not saying to steer clear of the 7k/5k switches, just be aware of what your expectations are and make sure your kit will deliver (ideally with close support from your VAR, preferably with documented deliverables!). The Nexus series appears to be the way forward, but it's not the trusty 6500 platform of yore quite yet. Granted, the 6500 has been allowed to mature for a long time (some would say too long), but there are a few issues on the Nexuses that are not worthy of a Cisco flag ship product no matter how you slice it.
In short, the 7k/F2 combo is a good product with a lot going for it. In a year or two with loving software updates it may even become great. As it stands I feel a tad cheated by Cisco SlideWare and the SE/VAR, but as we've got a sunset/horizon of about 10 years for this kit it might have improved significantly by the time it gets scrapped in favour of something Greater(tm) and we start all over again
I apologise if I hijacked the thread, but it's been a full day of smashing my face against the wall of "don't tell me this shiny new Nexus actually fails this badly at something that shouldn't even be an issue"