I've only delt with IBM and HP Blades as of this moment.

Blade server come in a chassis, that are a bit deeper than a standard server, because of all the cooling fans they have to put in the chassis. The IBM for example has 2 large rotary blowers with vents in the back. They will fit in standard rack, this is not the problem. Its the power that is the issue. Most data centers that where build from 99-02 can handle cooling of 65Watts Per SQFT , and now a days the new centers that are being built need to be able to cool 100-300 Watts Per SQFT, 300 being a bit excessive and 150 being a more real #.

You will find it very hard to find a provider who will provide you the 3-4 30AMP power ciricuts to one cabinet to power your 4-5 blade server chassis, let alone have them agree to cool that dense of a heat load. Technically speaking you can put 4-5 chassis in a rack.

Hope this helps.

There is a company called B-Line that makes a really nice 47U cabinet! Great for packing in the servers.