same problem here.
I'm using zeg 1.3.7 & have updated today to 1.3.7a (nightly)
thunderbird 3.1.9, sogo-integrator 3.105, lightning 1.0b2.105i, Conn. 3.105

imported my addresses from SnowLeopard 10.6.7, addressbook.
the import was before the update to nightly (1.3.7a)

I see the pictures on the web interface in the preview and detail, when opened the entry; and in thunderbird in the prview - but not when I open the entry.
the moment, I save an addr.entry in either web.-intf. or thunderbird, the pic. is gone.

ok, a bit more details:
I've removed the addressbook, which was imported from MAC under 1.3.7 and reimported it again under 1.3.7a.
looks good so far :)
I can edit and save contacts via web and they keep their pictures - well done. thank you!
even so, I get the following log.msg. from sogo, while the mac add.book connects:

sogod[1415] -[WEClientCapabilities initWithRequest:]: Unknown WebClient: user-agent='Adressbuch/875 CFNetwork/454.11.5 Darwin/10.6.0 (i386)

Apple MACOS 10.6.7
Mail 4.5 (1084)
Calendar 4.0.4 (1395.7)
Addressbook 5.0.3 (883)

still persisten is the problem with the sogo-integrator on thunderbird (icedove on debian).

some of the pictures, which are visible on the web-add.book, are not synced to TB-addr.book. the one which are synced, are only visible in the preview!
editing a entry with pic. does definitly remove it from that entry.

here a output from TB, while doing this:
*** new sync: 4
4/sync with http://192.168.98.6/SOGo/dav/sogo1/Contacts/personal/...
card set for upload: C9AEF95F-0C5C-464F-B831-24EA45791435-ABSPlugin.vcf
item: 4AE6F3C1-A696-41F1-A5E1-62DF9B8C8F2E-ABSPlugin.vcf; etag: "gcs00000001"; type: text/x-vcard
local version: "gcs00000001"
skipped
GETTING BUSY
no download needed
vcards.utils.js: file named 'C4C42B0E-9660-0001-3FA9-9F008BFC111A.jpg' cannot be read
0 card deletes to perform
updated card with key: C9AEF95F-0C5C-464F-B831-24EA45791435-ABSPlugin.vcf
uploaded card has etag: "gcs00000001"
RESTING
4/sync with http://192.168.98.6/SOGo/dav/sogo1/Contacts/personal/ has ended.

sogod logs this:
localhost - - [10/May/2011:21:29:34 GMT] "PROPFIND /SOGo/dav/sogo1/Contacts/personal/ HTTP/1.1" 207 421/175 0.018 1033 59% 0
localhost - - [10/May/2011:21:29:34 GMT] "REPORT /SOGo/dav/sogo1/Contacts/personal/ HTTP/1.1" 207 470/144 0.018 - - 0
2011-05-10 21:29:35.385 sogod[1415] <0x0x9f922a8[PostgreSQL72Channel]: connection=<0x0x9eefb20[PGConnection]: connection=0x0x9fd0278>>: message: WARNING: nonstandard use of \ in a string literal
LINE 1: ...791435-ABSPlugin.vcf', c_version = 1, c_content = 'BEGIN:VCA...
^
HINT: Use the escape string syntax for backslashes, e.g., E'\'.

localhost - - [10/May/2011:21:29:35 GMT] "PUT /SOGo/dav/sogo1/Contacts/personal/C9AEF95F-0C5C-464F-B831-24EA45791435-ABSPlugin.vcf HTTP/1.1" 204 0/432 0.138 - - 0
localhost - - [10/May/2011:21:29:45 GMT] "REPORT /SOGo/dav/sogo1/Calendar/personal/ HTTP/1.1" 207 125/245 0.013 - - 0
localhost - - [10/May/2011:21:29:47 GMT] "PROPFIND /SOGo/dav/sogo1/Contacts/personal/ HTTP/1.1" 401 0/232 0.003 - - 0

The problem is still there with 10.0pre2 and Thunderbird 10. I have several contacts with photos set on my iPhone or Apple Adressbook and they show up correctly in sogo connector but as soon as I edit anything on a contact, its photo disappears. I would say this is a critical bug.

Fixed in SOGo Connector for tbird 10. commit b7d588b94c4c59dbb951979fa695eceb93534292