Being down-down was great.
Apartment came with WiFi, and unexpectedly, a 4G MiFi dongle you could carry around with you during the day giving you on-the-go data "on the house" rather than your own data plan, was BRILLIANT / FANTASTIC.
Down-side of being down-town was a bar directly opposite the apartment that "got going" at 22:00, more customers on the street than inside, and didn't quieten down until around 02:00.
Travel advice. Depending on your arrival time (i.e. not late), from the airport jump on the RED metro line into town. Change at Alameda to the GREEN line toward Cais do Sodré. Jump off at Intendente, and make your way to the eastern side of the street (Avenue Alameda Reis) and the tram stop Igreja dos Anjos. From there, jump on a regular yellow north-bound 28E tram, which will quickly turn east and south, taking you down-town through some FANTASTIC initial impressions of the city. Jump off at the Calhariz - Bica stop, which is just 20 metres away from the apartment.
For days out, trains (which are really cheap!) to Sintra and Cascais should definitely be on your bucket-list. If you visit Cascais, then we'd definitely recommend hiring a CITY bike from Daniel at http://portugalrentbike.com/en/ and taking a ride along the coast road (and dedicated bike track) the beaches at Praia Grande do Guincho.
Enjoy - we did!