This is an excellent tool but it uses way too much memory. The memory limit for single user application seems to be 2GB on 32 bit Windows system (3GB for Linux?). At least for me the Perl process reaches this limit when cover is generating the HTML report from data that is roughly 120 MB after running ~400 test cases with Devel::Cover.
By commenting the Storable::nstore line from below pasted code, it seems to be possible to push the limit bit further. The subroutine is from Devel::Cover DB.pm module. Most likely this is not so nice solution and someone more clever can come up with better solution. But at least for me it seems to work.
It seems that you have to use the comment only when HTML report is generated. When test cases are run, this line needs to be in place. When HTML report is being generated, this line seems to double the memory usage. For example if the memory consumption was 1GB before this, this line will double it to 2GB.