WordPress themes come in two basic flavors...

• Free
• Not Free

Notice that for the second class, I didn't say paid...

Free themes would seem to be pretty self explanatory.  They don't cost anything.  But, what appears to be free isn't always.  Sometimes there is a non-monetary cost.  But let's talk about the themes that really are free.

There are theme designers out there that like to design themes.  They churn out a theme for themselves for a site and then kick out some variations for the world.  Sometimes (usually) they ask that you leave a link in the footer intact that comes back to them.  That is cool (look at the links on the bottom)...  They actually can get a little Google Juice from that, and it doesn't really hurt you.  I class those as great free themes.  I have used a few like that.  And even if I modify them... and I generally modify them... I leave the link to them intact because I think that is a great trade off. 

There are also some themes that have 'affiliate links' in the footer.  In this case, the designer is hoping that someone will click on the footer link and buy a product for which he will be paid a commission.  I actually have some affiliate links peppered around my sites for products or services that I use... and I am actually going to deploy a few more.  But again, you want to know who you are promoting on your site, whether it is your affiliate link or someone else's.

And there that are themes that you can download without spending money... but I don't really consider them free... they just don't cost money.  These are what may be referred to as "Sponsored Themes".  Basically, a company hires a designer to build a theme and allow it to be freely distributed.  There isn't anything wrong with that... it can be great for the people using the theme, designing the theme and paying for it. 

• The user gets a free theme that might be cooler than other themes out there.
• The designer makes money... feeds the kids.
• The sponsor gets links back to their site, Google Juice and traffic.

But, the problem is that some of the sponsors might not be people you want linked on your site.  Most are just fine... but there are all sorts of companies.  Here is one that is sponsored by a web host.  I have run across themes sponsored by porn portals and even real estate companies... I don't want either linked on my site... especially the real estate company (the Google Juice would actually be stronger for them because of the relevance of my site). 

What can you do about it?

There are three things you can do...

• Only deal with premium, paid themes.
• Limit yourself to themes that don't have objectionable links.
• Kill the links.

I do the first two.  I have a paid theme from Shifter on my primary blog.  I have several free themes with limited links on property blogs and other websites that I administer (my wife's law firm and our business and family sites).  I don't kill the links.  There is a variation that I have run across... but I wouldn't personally do it... masking the links.  Basically, they can be masked by making the the same or similar color as the background.  I would avoid that for two reasons.  It is certainly against the spirit of the Terms of Service you likely agreed to when you utilized the theme, and Google doesn't like hidden content. 

So, while you are wandering around looking at the thousands of free theme options, be sure to scroll down to the bottom of the demo and take a look.  Also, when you test the theme on your own site, be sure to look at the footer and follow the links.  Know who you might be promoting with your business.

***Update***

I realized that I wasn't very clear.  This discussion pertains to WordPress in the self-hosted variety... WordPress.org, not WordPress.com.