Stayed here in March last year on a boys trip for the rugby at the RDS, had a great time.
Stayed here again in the summer with my wife and two kids (11&8), again thoroughly enjoyed.
The hotel is located about a 15 min walk to Grafton St and likewise a 15 min walk in opposite direction to RDS for the rugby. For those that don't want to walk there is a taxi rank outside, or just at the end of the road numerous frequent buses.
I found the hotel staff very friendly on both my visits, we had a nice breakfast and the bar serves a cracking pint of Guinness and is very welcoming.
There is a starbucks next door for the coffee lovers and plenty of bars and restaurants within a few minutes walk. In fact when I was with the lads we preferred the nearby bars at Baggot St/Merrion Row to the overpriced Temple Bar.
For family trips I recommend the Dublin Pass for access to the visitor attractions and also worth considering pre booking bus passes for the duration of your stay. If you with kids a trip to the Zoo and the Aquazone are well worth it. You can catch bus from near the hotel or from St Stephens Green to most attractions.
Ten of us have booked to stay at The Mespil again in May for the rugby.

Stayed in the Mespil on a whim for the new year, stayed 2 nights and was plesantly surprised. The hotel is located about 10 minutes walk from St.Stephen's Green, which is ideal. The room was clean, warm and we got a great night's sleep as it is lovely relaxed hotel. The hotel bar has a chilled out vibe and although we didn't eat at the hotel, the menu looks good. Beside the hotel are a little row of restaurants / coffee houses. This hotel was great value as well, and i will definitely be staying here again when i head up to the capital

Stayed for 5 nights in Dec2012-Jan 2013. Good location , about 15-20mins walk from the city centre but there is a bus stop round the corner so no problem if you don't want to walk (€6.50 bus day pass).
Our room was quiet, clean and really comfy.
Wifi is available throughout hotel and is fast enough . You can also use computers with Internet downstairs and it is free plus if you need to print something there is a printer available.
The staff is very helpful and friendly .
Unfortunately didn't have a chance to use their restaraunt because after reading trip advisor reviews we decided to try Thai take away few metres away from the hotel: it was really good ( surprisingly there were no Thai staff working in that place but whatever nationalities they are they do a very good job!)
Would recommend!

We stayed here using an online deal which was amazing value.
The staff are welcoming and friendly and helpful and smiling always.
The rooms are spotless. The bathroom was immaculate. Lots of hot water. Free hotel parking.
The breakfast was yummy. Lots of everything. Although a buffet, it was hot and freshly cooked. I had fresh fruit scones that were divine.
Great location. Walk into city in 15 mins. no need for taxis.
Would stay here again for sure.