Thanks for all your replies.

Although it would normally be very unusual for me NOT to use a clustered index (yeah, yeah, i've been there, done that, got the t-shirt) I do find it hard to believe there's not a table size where it's actually beneficial not to bother (1 row even?).

When I get a spare moment i'll jump on a test server and try it out with varying levels of data and see what the execution plan says!