I really hate unless (cond) { ... } else { ... } constructs. I think they're better written as if (not cond) { ... } else { ... }. It could be I'm an old C programmer, but I find it easier to follow.

More importantly, I think your code will fail to process the last record. I would do something like the following:

my @record;

while( <FH> ) {
    chomp;
    if( /start-delim/ ) {
        @record and process( @record );
        @record = ();
    }
    push @record, $_;
}
@record and process( @record );
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If there was an end delimiter, the loop could be flipped around to a do/while, and one could do away with the two calls to process().

I note in passing that davido's idea of setting $/ is excellent, but it onlys work if the delimiter is a fixed string. If you need an RE to match the delimiter, a different approach is also possible.