We stayed at the Jolly Villa Carpegna in mid-July, and overall we were pleased, and would stay there again.
The Good:
- We liked the location. We took the #31 bus to Cipro subway station (on the A line), which is only one stop from Ottaviano/Vatican stop. This worked well for us, as most times we only had to wait 5-10 minutes for a bus, although the weekend waits were a bit longer. The A subway line also had stops for Trevi, Termini, etc.
- The hotel and the rooms were clean and up to our standards.
- The pool was large, refreshing and a wonderful way to cool down after hoofing it around Rome on a hot summer day!
- Exercise room was small but well-equipped.
- Morning breakfast buffet was very extensive--very impressive.
- Front desk staff were mostly helpful, in our experience.

The Bad:
- We had a King size bed, which was actually 2 Doubles put together, which is not the most comfortable.
- Shower only had the half-door glass partion, not a full curtain.
- Cleaning staff were pretty stingy with the # of towels.
- Internet options were limited. Wireless did not reach up the 3rd floor, plus you had to purchase access codes at the front desk, which cost 15Euros per hour.

My husband and I stayed at Jolly Hotel Carpegna for six nights. The rooms are large compared to many hotels within the central part of Rome. Breakfast was very plentiful each morning. The front desk was very helpful whenever we had questions. We caught the 571 or 916 bus (bus stop is about 4 blocks from hotel not far from the McDonald's) daily to visit the monuments. The swimming pool was very nice to cool off in after sightseeing. We had previously stayed at this hotel in 2005, and were drawn back to it because of the size of the rooms and the many amenities that the hotel offered.

Our young family stayed at the Jolly for 5 nights in mid summer, having been strongly (and correctly) advised that pool & aircon were almost mandatory for travelling in kids in Italy at that time of year. We found it a pretty good value compromise. Basically you get the pool, ac & decent rooms for a good price. However you also get the pain of being well out from the centre of town: it's around 2kms west of the Vatican. Nearest Metro is a 15 minute walk up a hefty hill, so most residents stick to the nearby buses to get into town. These may or may not come quickly, can be hot in the summer, and will still take 15-20 mins to get anywhere interesting. Taxis are quick to arrive, but at 10 or 12 euros each way, get expensive fast.

Likes:
Quiet rooms: double glazed (yet openable) windows.
Well behaved aircon
Friendly staff throughout the stay.
Decent breakfast

Dislikes:

Pain of getting into the centre.
Expensive restaurant, with not much else close by.

The hotel is quite new and has very well appointed, clean rooms. Food is good as well.
The only problem is location. It is actually not that far from city centre, as you can get to St. Peter's and the Vatican by a single bus ride. However, as the hotel can be only be reached by bus or taxi, the bustling and chaotic traffic of Rome does make the difference. Timing is really unpredictable as a short ride normally taking 15-20 minutes may become a nightmare lasting over 1 hour at peak hours and/or inclement weather.
In the end, it is a very good business hotel. If you are visiting Rome for sightseeing other than cars and traffic, you should better search for a different option where commuting by car or bus to major attractions can be avoided.