I do have an account at Lending Club that is < 2% of net worth. I'd echo what others have said that it does take a little bit of time to purchase new notes, and I would not feel comfortable having more than 5% or so of my net worth in such an account.
All of my other investing is very hands-off (index funds), so I view it as a fun way to invest a bit of "play money". After setting up my filters, logging in every once in a while at one of the times new notes are added (6am, 10am, 2pm EST) makes it very easy to find enough notes that meet my criteria and it takes less than 5 minutes a week and I find it kind of fun. Almost all notes that meet my filters are snapped up fairly quickly, so logging in at any other time of day yields nothing.
I've heard that the tax consequences can also be annoying to deal with, but I am using a portion of my Roth IRA and therefore don't have to worry about it since it is not a taxable account.
On balance, I'd agree that it is probably not worth it unless you enjoy looking at the stats and playing around with the account for a few minutes every week. Even then, I'd be cautious not to over-invest.