Since my distribution of choice updated to PHP 5.4 a while ago and the first modules of the old PHP 5.3 started to fail due to missing dependencies I had to update my server to PHP 5.4.
Since the last “official” blogtng version uses sqlite2, which was removed from PHP 5.4, it doesn't work anymore. Fortunately there is a version which has sqlite3 support as an extra branch on github (download it here).
to use this version instead of the old one move the old blogtng directory in lib/plugins of your dokuwiki installation out of the way and unzip the downloaded file there. Rename the created directory to blogtng.
Next copy over all your templates from the old blogtng-directory to the new one (they are inside the subdirectory tpl).
Last step is to convert the database. The database is in the directory data/meta of your dokuwiki install. The blogtng database is named blogtng.sqlite. You need the old sqlite2 binary (named sqlite on my system) and the new sqlite 3 one (name sqlite3). Here is the command for the conversion (run it inside the meta directory):
sqlite blogtng_old.sqlite .dump |sqlite3 blogtng.sqlite3
After this the Blogtng should run fine with PHP 5.4 and the sqlite3 extension.
So far my site seems to work just fine, but if you find anything that doesn't work please let me know.