Pursuing theology degrees online has increased along with the increasing popularity of online eduction as a whole. The increased availability of high-speed Internet connections along with the viability of video conferencing and the like has made such education far more feasible. While there are a lot of positives associated with online education, there are some potential downsides that any potential student should know.
While there are some quality online theology programs offered by accredited schools (see some recommended ones here), you have to be cautious when looking at online degrees because many online programs are not accredited by a respected accrediting agency. Sure, they may be "accredited" by Billy Bob's Bible Accreditin' Agency, but that doesn't mean the accreditation is worth anything. If a school lacks regional accrediting by one of the six major agencies or by ATS (the Association of Theological Schools), avoid it all costs.
Speaking of costs, that's another obvious (and crucial) factor in your decision - cost. Some schools charge the same for online courses as they do their traditional, onsite courses. Others charge substantially more (in theory, to cover technology costs). Perhaps even more importantly, while most schools provide loan assistance to online students, not all provide scholarship or grand assistance. As such, it's important to check out the financial viability of the program before you get your hopes up.
To state the obvious, not all programs are created equal. If you're absolutely committed to pursuing your theology degree (whether undergraduate or graduate), you need to consider the reputation of the institution. Personally, I would only consider schools that have a reputable onsite program and where "regular" faculty are responsible for the teaching. Otherwise, you'll be in danger of participating in an inferior program.
When you're investigating a program, you want to make sure that you will be able to enjoy the same course offerings as a traditional onsite student. Some programs simply do not have the resources to offer the same level and range of courses as they do in their traditional programs. If this is a problem, you may want to consider a hybrid program where you take the majority of your courses online but are able to take onsite courses as needed.
Another possible downside to pursuing theology degrees online (or any online degree, really) is the possibility of isolation. Speaking from experience, one of the greatest joys of both my undergraduate and graduate degrees was being around others with similar interests. Some of my best friends in seminary were even folks who had very different views on serious issues than I did personally, but we learned how to disagree (mostly) respectfully.
In the end, you have to make the decision that best suits your needs, interests, and background. It's just important to know the pros and the cons before you sign the check.