> I was under the impression that even though TLS has the idea of built-in compression, in practice, that is never actually used.

This is determined mostly by the browser. Most browsers in TLS ClientHello send an empty compression algorithm list since they will use encoding headers (which let the servers cache the compressed data). A browser using Spdy could indicate it supports deflate to enable compression.

> Also, you claim that Google is basing this protocol on assumptions and you imply that they do not understand the value of metrics. I strongly disagree with this sentiment

Watch the tech talk video the other guy posted and drink when they say 'we assume' or to that effect. These guys do testing to confirm their assumptions. Take a look at when a questioner asks about high packet loss and how they hand-wave away Spdy being crippled by high packet loss.

> because SPDY headers are length-prefixed for ease of parsing. It compresses better when the prefix is included in the dictionary; such that {0x00,0x00,0x00,0x07,o,p,t,i,o,n,s,} would compress to one byte, not 5

No, wrong, that's not how compression works. Deflate uses lz to compress runs and repeats like \0\0\0 and it uses huffman to better encode it to bits.

Here's a clue for you, compressing "\0\0\0\7options" using deflate:

    spdy prefix: 7 bytes
    w/o repeats: 6 bytes
    w/o any counts: 6 bytes

The first is the rfc draft dictionary, the second is that with only the first occurrence of each count, and the third with on \0\0\0 at the start and no other counts.

Not even to mention there is limited space in the prefix due to the window size and it sliding, so not only are the counts basically useless but they use space that could be used for other data.

I take it back... these people don't just lack rigor, they are clueless bordering on incompetent. As just an implementer I can accept that you don't completely understand the issues and are excited to work on the implementation, but as protocol designers from Google the work done with Spdy is just unacceptably bad.