I find HTML messages totally unreadable when I receive digests from mailing lists. But then if the mailing list manager makes MIME coded digests, I have no problems. Unfortunately, a lot Linux mailing lists are running on mailing list managers which don't seem to be able to make MIME coded digests. (Linux Bangalore's lists, on yahoogroups.com, are among them). Those become a royal pain to read.
IIRC, linuxers digests can be received in MIME encoded format but it is disabled by default. That option has to be enabled explicitly in your subscription prefs.
In fact, I'm getting Linuxers digests correctly MIME-encoded, and that makes things very easy for me. You're right about Linuxers. It's the Bangalore groups which work through yahoogroups.com, and I can't seem to find any way to switch on MIME-encoded digests. Now of course, I can't even get access to groups.yahoo.com, so I can't even experiment. We're beginning to become a country as bad as China when it comes to censorship.
Shuvam