Alpha specific bugs are marked in the bug tracking system using the "usertags" mechanism (http://lists.debian.org/debian-devel-announce/2005/09/msg00002.html) with user email@example.com. The tags are:
ftbfs -- Fails to build from source
broken -- unusable on Alpha
buggy -- buggy on Alpha
maybe -- might be Alpha specific, but this has not been verified (might be just a generic 64-bit bug. Somebody with an AMD64 should check these)
hardware -- This requires particular hardware to be reproduced.
The result can be seen here: http://bugs.debian.org/cgi-bin/pkgreport.cgi?tag=ftbfs,broken,buggy,maybe,hardware;firstname.lastname@example.org
debian-installer bugs are not tagged, since they can be found at http://email@example.com;include=alpha.
Also not tagged are the bugs of the following Alpha-specific packages:
(add kernel packages here)
FTBFS can be checked at http://buildd.debian.org/status/architecture.php?a=alpha