Accessibility for Search Engine Bots in Organic Search
It's not uncommon on websites to use forms for various functionality. For instance, store locators on websites are often form-based, having site visitors enter a Zip Code into a form and returning results based on the values in the form field. But it's easy to forget that search engine robots, while trying to mimic human behavior, alas cannot fill out forms like humans. This often means that indexing robots also cannot index the information housed behind the form, often leaving hundreds or thousands of valuable web pages unindexed because the form served as a brick wall to the indexing robot.
A common example, as I mentioned, are store locator functions on websites. These often ask that a Zip Code (or some other geographic identifier, like city and state) be entered into a form to filter the store locations down to just those located in your local area. However, a search engine robot doesn't have a Zip Code and can't complete a form. So how can it get to those store pages?
If, as in the store locator example, you need to use forms on your site but also need the pages behind those forms indexed for organic search, there are two ways to provide a "conduit" for search engine bots to avoid the form and find the information.
First, you can always provide inbound links from other websites directly to those pages. For instance, you might put a link to a particular store in a directory for that town's chamber of commerce. Or there may be a mall directory for the mall your store is located in that provides an inbound link. However, the problem with inbound links is that they reside on someone else's website --- often a website you don't control. That link could disappear at any time, which is why I also recommend the next approach.
You should consider adding a sitemap to your website (if you don't already have one). You can locate the sitemap in the footer of your pages so that it's unobtrusive, but it's there in case people, or search engine bots, need it. Then put the links to the content behind the foms in the sitemap. If you have a store locator, perhaps have a listing of all of the store pages.
Conversion Measurement from Paid Search
I recently ran across a client's website form that, when submitted, generated an AJAX popup thank-you message instead of directing the form submission to a separate thank-you/receipt page. Functionally that works fine, and it can for paid search tracking too. Just be aware that if you use an AJAX popup thank-you message for your form that you also alter that AJAX to add the search engine ad tracking code. Otherwise, your conversions won't be tracked properly.
Goal Measurement in Google Analytics for Both Paid and Organic Search
One problem for both paid and organic search with forms comes from goal tracking with Google Analytics. Unlike paid search that has simple conversion tracking code to measure campaign success, organic search conversion measurement relies heavily on applications like goal tracking in Google Analytics to truly understand how organic efforts are meeting your goals and driving conversions.
In the previous example, I mentioned the use of AJAX popups as thank-you/receipt pages. While these may look nice for usability purposes, they also put a kink in Google Analytics goal tracking. Google Analytics goal tracking relies on visitors reaching specific URLs on a website to track a goal as it is achieved. In other words, Google Analytics needs to know the URL of the thank-you page in order to log a goal as met. If you use an AJAX pop up thank-you message, however, the URL of the page doesn't change, therefore making it difficult to track the goal in Google Analytics.
One solution is to use the event tracking code, which you can add to your submit button and then tracks a button click as a goal being met. This approach is commonly used for counting goals where files don't allow Google Analytics code to be inserted, such as on a PDF file download.
But what if you have form validation on your form? If a visitor doesn't fill out the form correctly, the goal is still tracked. If the visitor takes several tries to fill out the form correctly, each click on the submit button will be a goal met. So while the event tracking is helpful in some cases, it can also lead to inaccurate goal tracking.
Ideally, you should use a standard Web page instead of an AJAX popup for your thank-you/receipt page. There are other reasons that this is a good idea (including the next segment), especially because it helps ensure more accurate goal tracking in Google Analytics.
Google Website Optimizer for Both Paid and Organic Search
Finally there's the issue that forms can create for Google Website Optimizer tracking. If you use Google Website Optimizer (GWO) for A|B or multivariate testing on your landing pages or website, you know that, similar to Google Analytics, GWO uses actual URLs of pages to determine if a conversion has been attained. However, if, as in the previous examples, you don't use a traditional thank-you/receipt page upon form submission, you may not be able to do testing with GWO.
Whatever your challenge with forms, be sure to think through the challenges before programming your form to ensure indexability, accurate tracking, and testing ability!